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Illustrated Self-Guided Course On How To Use The Slide Rule

363 points by ngram 6y ago

surajs 6y ago
how eccentric! would much rather prefer a yt vid / tutorial pls.
- TallGuyShort 6y ago
  Such tutorials are readily findable by searching for "slide rule tutorial" on YouTube.
- toolslive 6y ago
  I think the preference is age related: Personally I prefer text over video, as I can process it at my speed, while with video I'm limited to the speed with which it's explained. My children all seem to prefer video.
  - ghaff 6y ago
    You're almost certainly right. I hate searching for info on something that could be easily explained in a paragraph and maybe a screenshot and instead I have to watch through some video--usually with an ad. I confess that I really resist making videos of things unless I have no choice but I know a lot of people prefer them. A well-written and illustrated explanation like this one? I can't imagine preferring a video unless someone just wants some background noise and they don't really care about understanding the subject.
  - JadeNB 6y ago
    > I think the preference is age related: Personally I prefer text over video, as I can process it at my speed, while with video I'm limited to the speed with which it's explained. > My children all seem to prefer video. When I ask for text transcripts of our training videos, in place of having to sit through 20 minutes of poorly acted out skits (that, re-certification being a periodic thing, I have sat through some 5 or 6 times already in my 10 years on the job), I am always told "but people enjoy the videos"—as if providing transcripts were somehow exclusive of providing videos.
bregma 6y ago
When I was in university, if you forgot your slide rule at an exam they kindly had a supply of log tables you could pick up from the proctor.
stblack 6y ago
One of the nicest things about a slide rule is, you can easily see the sensitivity of the result to variations of your last input. With a calculator, you get precision. With a slide rule, you get a value and its sensitivity.
KineticLensman 6y ago
Alas! No specific mention of the circular slide rule [0]. I have one in my desk drawer that I inherited from my dad - who used it in the 1970s to confirm his hip hacker credentials to his colleagues (they were building the control circuits for early radio-therapy machines in a cancer research institute). [0] https://americanhistory.si.edu/collections/object-groups/slide-rules/circular-slide-rules https://americanhistory.si.edu/collections/object-groups/sli...
- analog31 6y ago
  I was curious about circular slide rules, and found one on eBay for a few bucks, so what the heck. It turned out that it was a give-away from a company that used to be in my town, so I ended up having a nice conversation with the seller about his history with the company and so forth. He was a long retired engineer. Anyway, I started playing with ratios, and noticed that the thing is inaccurate! Further inspection and hypothesizing led me to discover that the scales were not printed concentrically with the mechanism. It's very slight, and not critical to my work in any way, so I treat it as part of the learning experience.
- dan-robertson 6y ago
  Circular slide rules tend to have smaller scales which may be harder to read but being circular has a great advantage. Look at how much effort in the OP is devoted to cases where the answer would ordinarily be off the end of the scale.
- psim1 6y ago
  Still very much in use: the E6B! https://en.wikipedia.org/wiki/E6B https://en.wikipedia.org/wiki/E6B
- dctoedt 6y ago
  My dad was a USAF fighter pilot; he kept his in-flight circular slide rule around for years. Unfortunately I didn't see it around when clearing out the house out after he and my mother died; I know I'd have kept it (because I've still got my yellow Pickett aluminum Model N-500-ES, © 1962).
derekp7 6y ago
One under-appreciated aspect of a slide rule, is for instantly seeing fraction reductions at a glance. For example, lets say I want to find out what aspect ratio a given screen resolution is at. I can set that resolution as a ratio on the slide rule's C/D scales (i.e., 1680x1050 becomes 1.68 one C, lined up with 1.05 on D. Then I glance over, and see immediately that is 16 x 10 resolution.) If the value goes off the scales, look up to the CF/DF scales. This is also great when you have a bunch of resistors and capacitors, and you need to build a circuit where the two are at a particular ratio. Set the ratio you want, then you can take whatever resistor you have, and see if you have a cap that is "close enough" to what you need.
- KineticLensman 6y ago
  > This is also great when you have a bunch of resistors and capacitors Yes! This is the sort of thing my Dad used them for (see my other comment here for the context)
- kqr 6y ago
  Also ratio multiplications, e.g. when increasing the amounts of ingredients in recipes to match a particular amount of something. So if the primary ingredient is chevre cheese, the recipe calls for 180 grams, but you can only buy it in 250 gram packages, you can set the slide rule to "180 over 250" and then just mechanically read off the proportionally correct amounts of all other ingredients. Slide rules are indispensable in the kitchen to me and I'm surprised they're not part of standard kitchen equipment like e.g. scales. Edit: Similarly, if the recipe is expressing ingredients in US units and you would want to know the international amounts, you can set the slide rule to the conversion ratio and again, mechanically read off the correct amounts as you go.
  - gumby 6y ago
    This is one advantage of the customary (English language non-metric) units: the common ones are full of rational factors (1/2, 2/3 etc) — it’s pretty easy to adjust a recipe to the number of people.
- myself248 6y ago
drfuchs 6y ago
Another great thing about slide rule days is that results are naturally constrained to 2 or 3 significant digits, so you'd never see nonsense like "The mountain is 10km high, or 32808.4ft" as if the 10km figure was accurate to 6 significant digits.
- INGELRII 6y ago
  Unnecessary accuracy is technical incompetence.
  - ghaff 6y ago
    I think you mean precision in this case. If you're going to be all high and mighty you should probably get your facts correct.
- sirsar 6y ago
  I still remember the day I found out the "98.6 degrees" human body temperature was just an oversignificant conversion from "about 37 C, or maybe lower."
  - JadeNB 6y ago
    > I still remember the day I found out the "98.6 degrees" human body temperature was just an oversignificant conversion from "about 37 C, or maybe lower." Really? According to Wikipedia, the Fahrenheit scale (https://en.wikipedia.org/wiki/Fahrenheit#History https://en.wikipedia.org/wiki/Fahrenheit#History) is about 18 years older than the Celsius scale (https://en.wikipedia.org/wiki/Celsius#History https://en.wikipedia.org/wiki/Celsius#History), and I'm surprised that human body temperature wasn't included as a calibration. (But of course the fact that I'm surprised by it doesn't mean it isn't true!)
    - _underfl0w_ 6y ago
      Could've sworn I remember hearing in grade school that one of then was actually calibrated with cow body temperatures. Don't remember which scale, though.
leetrout 6y ago
Circular slide rules are still used today in aviation in the form of the E6B flight computer. https://en.m.wikipedia.org/wiki/E6B https://en.m.wikipedia.org/wiki/E6B
- ghaff 6y ago
  Back when slide rules were still widely used and even after calculators had recently come in, you also saw a lot of industry-specific cardboard sliding scales that were basically slide rules with different types of units.
dave_aiello 6y ago
In an era marked by renewed interest in vinyl records, shouldn't there also be a corresponding interest in slide rules?
- coldpie 6y ago
  I dunno, man. I'm pretty well-versed in math and I find this page kind of baffling. I'm sure it's one of those things that is very easy to use once you learn it, but at least this introduction is very daunting. To do a basic multiplication (step 1 in the linked page) I need to use the C and D scales, each for two different purposes. Why not A and B? How do I remember it's C and D? Which part goes on C and which part goes on D? Then step 2 describes what to do if it goes off the edge of the scale, and it involves making an approximation. How do I know how accurate my approximation must be? Why is it to the tens digit? If I get larger numbers do I continue to use the tens digit, or some higher factor? We're only on step 2 and I'm already lost. This definitely looks like a great tool, and I'm kind of sad I don't have one or understand how it works, but this kind of complex learning and memorization up against dropping a needle on a record you like isn't really a great comparison.
  - yuubi 6y ago
    It works better if you know how the scales are constructed and get familiar with properties of logarithms (mainly variations on log ab = log a + log b) C and D are plain log scales, where one decade is the length of the rule. They're sort of the default scales to use. Multiplication is commutative, so you put either number on either scale. The important thing is that the distance from the left index of the scale is proportional to the log of the number (reading the scale as 1 to 10), so you want to arrange the scales to add the lengths corresponding to your numbers such that the lengths add up. (Or so that you subtract the length of the divisor from the dividend, if you're dividing). You can get by without the approximation if you're willing to set up the multiplication, see that the product is out there in thin air, then move the slide to put the right index where you originally put the left index. (3 times 5: on the d scale find 3 and put the left index of the C scale there; opposite 5 on the C scale read nothing because there's no D scale there; try again using the right index of the C scale, which is the same thing as having another copy of the D scale out there to the right where the air was). A and B are each 2 copies of a log scale. You can absolutely use the left side of A and B for your numbers to multiply, and the product will always be on the scale. People normally use(d?) C and D because the precision is better and because the rest of the scales (like the trig and log-log) are constructed to work with them.
agumonkey 6y ago
Fascinating near invisible yet very high abstraction.
ghaff 6y ago
Slide rules to calculators was an incredibly fast technology transition for the sort of people who would have been using slide rules in the first place. A 5-function calculator was about $100 in 1974 (so about $350 in current dollars) and an HP scientific calculator was 3 or 4x as much. By about the next year, a TI scientific calculator was about the same and by a year or two later you could get an HP--which was the gold standard for about the same amount. And that was around the price point where making them not just OK to use but mandatory was reasonable at least in higher ed. I was one of the first classes in college where calculators were the norm and slide rules were maybe something you brought for backup at exams. (Calculators were still LEDs so you had to keep them charged.)
code4tee 6y ago
The “E6B Flight Computer” is a slide rule designed to perform various navigation calculations and is still a part of flight training for many pilots today. Once mastering it the old way student pilots are then allowed to use electronic versions or iPad apps that do all the calculations instantly.
lokedhs 6y ago
I'm of the generation that missed out on slide rules by a decade or so. My parents had one thta i played with as a kid, and I learned to do multiplicication and division with it. I'd like to get one now, mainly for fun, but if you want to buy one on Ebay in good condition, you have to pay quite a bit of money.
- ghaff 6y ago
  Plastic "student" slide rules are cheap on eBay. But, yes, quality K&E's etc. are expensive.
  - lokedhs 6y ago
    Since this is something I want to keep on my desk, not only for decoration but for actually copute things if I'm bored, I really want tone of the nicer ones. It seems around 35 EUR is a normal price.
    - ghaff 6y ago
      Quality slide rules probably cost a lot more than that when they were still being manufactured :-)
  - dwheeler 6y ago
    Quality K&E's were never cheap :-).
- myself248 6y ago
  Seems to me that this is also a lovely use for a desktop laser cutter. Dig out a copy of Pynomo or something and make your own scales that suit whatever specialty application you have in mind.
  - 082349872349872 6y ago
    Came here to say nomograms are slide-rule-adjacent. https://en.wikipedia.org/wiki/Nomogram https://en.wikipedia.org/wiki/Nomogram
reaperducer 6y ago
I'm old enough that I had a slide rule when I was in school. Everyone did. They were built in to our pencil boxes. Most of us didn't use them, except the fancy-pantses who also insisted on using mechanical pencils. But we all knew how to use them. I'm graybeard enough that even through college, electric calculators were prohibited in class because they would give you answers without helping you understand the problem.
- qrbLPHiKpiux 6y ago
  > answers without helping you understand the problem This is my problem with common core math. It shows how to get to an answer, but I feel it bypasses fundamental understanding on why the answer is what it is.
  - metiscus 6y ago
    I feel that common core focuses more on teaching the various methods than embracing the idea that correct answers and understanding are largely what matter rather than any specific method.
    - ghaff 6y ago
      That's hardly a new thing with common core. See Tom Lehrer's "The New Math." "...But in the new approach, As you know, the important thing is to understand what you're doing, Rather than to get the right answer."
      - metiscus 6y ago
        Interestingly that song is apparently about the first time they tried to massively redesign the mathematics curriculum based on on fuzzy math that we were falling behind the Soviets or whatever. My parents tell me they rebased around set theory early etc but it foundered on nearly the same rocks that common core mathematics is now - teacher must be well educated in the pedagogical paradigm and fully understand it. E.g. you can't just take the same set of teachers from math v1.2.1 and slam them into math v2.1.0 or whatever without significant issues the two approaches are not abi compatible. That's why in my with opinion common core we are seeing teachers test finding answers via method 1 specifically or method 2 specifically rather than encouraging the use of either to get a correct answer by an understood method. /rant
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wdb 6y ago
Cool, now I finally know how to use this rule that I got when me and my siblings were clearing up the family house after my parents passed away. It's really fascinating, I will show my nephews when I am back in the home country :) Thanks for posting!
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vilesolid 6y ago
See the 18 proven ways on how to make 10 dollars a day online (2020)? https://vilesolid.com/how-to-make-10-dollars-a-day/ https://vilesolid.com/how-to-make-10-dollars-a-day/
ColinWright 6y ago
A few years ago I met Fred Haise Jr and got him to sign one of my Slide Rules. He was so excited to see it, took it from me, and started to show the event host how to use it! He asked me what I use to lubricate it, and when I said "Pencil graphite" he got even more excited. Apparently a lot of the other astronauts had used fancy light lubrication oils, but he always used a pencil and never had any problems. He was a lovely man, and it was fabulous to enthuse with him over this wonderful piece of technology.
- mcguire 6y ago
  Powdered graphite is an excellent lubricant that doesn't attract crud. My father had a little squeeze tube of it for locks; it eventually ran out and I haven't seen any more since.
  - philiplu 6y ago
    You can find the small tubes at hobby stores, with the supplies for Pinewood Derby cars for Cub Scouts. I went through several tubes during my son's years in Scouts.
    - avhon1 6y ago
      You can also get it at hardware stores for lubricating locks.
      - EricE 6y ago
        The versions for lubricating motorcycle cables are finer and less messy than the cheap stuff they sell for locks. If you want to be neater with your slide rule, anyway :)
philiplu 6y ago
What a blast from the past. I can draw a direct line from my encountering a slide rule to ending up as a programmer. I owe my career to that device. I was a nerdy 10 year old kid who liked doing arithmetic in 1970, but didn't know anything particularly advanced. I convinced my parents to get me a slide rule as a Christmas present that year; a basic white Post model 1447 - I know that because I'm looking at it right now. It's been in my desk drawer forever as I could never convince myself to throw it away, even though I've long since lost the sliding cursor. Anyway, I got the slide rule, had fun with basic multiplication/division, but didn't understand what the S, T, and L scales on the back were for. Sine/Tangent/Logarithm? What are those? Off to the library, where I picked up a Tutor-Text book [0] on trigonometry, discovered I'd better first learn some algebra, picked up another Tutor-Text book on that, and began a two-year tear teaching myself algebra to integral calculus. Which meant I tested out of a couple years of math in high school, ran out of courses to take, and in my junior year was allowed to walk to the local college to take 2nd year Calc classes. At that college, they started letting me play with the computers, both an IBM 5100 APL machine over one summer, and hands-on access to the IBM 11/30 clone minicomputer that was the main machine. The math prof pointed me at Knuth's "The Art of Computer Programming", and that began my transition from pure mathematics to computer programming/science instead. I even wrote a MIXAL assembler/MIX simulator for the minicomputer that the college ended up using to teach an assembly language course. So thank you, Post, Pickett, K&E! And Tutor-Text as well. [0]: https://gamebooks.org/Series/457/Show https://gamebooks.org/Series/457/Show
- ezequiel-garzon 6y ago
  Thanks for sharing such a wonderful story. Something tells me your career path wouldn’t have changed significantly if you had never touched a slide rule, though :)
- neilpanchal 6y ago
  > So thank you, Post, Pickett, K&E! And Tutor-Text as well. I didn't even grow up in this era and I keep buying stuff from eBay purely out of fascination for old ways of doing things. These names on all kinds of things I have horded - architectural templates, drafting machine, cutting mat, compass set, lettering templates, etc. Thanks for sharing your story!
Bloggerzune 6y ago
A well-written and illustrated explanation like this one? I can't imagine preferring a video unless someone just wants some background noise and they don't really care about understanding the subject. https://www.bloggerzune.com/2019/10/a-bloggers-big-mistakes-part-2-blogger.html https://www.bloggerzune.com/2019/10/a-bloggers-big-mistakes-...
tzs 6y ago
One unexpected advantage in some circumstances of a slide rule over current portable computing devices is that it does not have memory. You are allowed to bring a calculator to ham radio license exams in the US, but you have to clear its memory (both data and program memory for programmable calculators) first. If the examiners aren't sure you have done so, they are supposed to disallow the calculator. Unlike many other standardized tests, there is no specific list of what calculators are allowed. I brought my HP-15C, but wasn't sure that the examiners would be familiar with it and so wasn't sure I'd be able to convince them that I had cleared it. I also brought a slide rule. That way if the examiners disallowed my HP-15C I'd still be covered. They did allow the HP-15C, and it turned out that even though I took all three exams (Technician, General, and Extra) that day, I only actually used the calculator once. The questions are all multiple choice, and there was only one where a quick mental approximation wasn't enough to identify the right answer.
- Someone 6y ago
  Nitpick: a slide rule does have memory, but it is small and gets cleared when doing computations. One typically can store one number by moving the slide and another one by location of the cursor. It also is fairly hard to hide the fact that the memory isn’t cleared. Many slide rules also have some read-only memory, for example ’storing’ the constant π.
ssimpson 6y ago
I've been trying to figure out how to use my grandfathers Dietzgen Maniphase Multiplex Decimal Trigtype Log Log rule. I found the manual on this site! Very cool!
dylan604 6y ago
One of my favorite scenes in "Apollo 13" has a CO2 hazy Jim Lovell asking Houston to double check his math, and it cuts to a room full of engineers as they all grab their slide rules to calculate the answers Jim had just done in his head/scratch pad.
xenocyon 6y ago
As someone who grew up in India in the 20th century: slide rules are unfamiliar, but we used log tables (calculators of any kind were prohibited through high school and standardized tests). For those unfamiliar, log tables serve to replace multiplication/division of floating-point numbers with addition/subtraction instead, making scientific computation a lot easier. The main benefit of introducing this friction, rather than allowing calculators, is that it (a) encourages one to do simple calculations by hand, and (b) gets one in the habit of quickly double checking that log-table-based results fall in the correct ballpark. Calculators induce a sort of mindlessness where glaring orders-of-magnitude errors pass us by since we expect the machine to get it right. With all that said, I don't know that I would recommend the use of log tables to high schoolers in the 21st century. That effort might be better utilized on more pressing needs e.g. statistical literacy. Many folks (including me) got entirely through STEM-focused high school knowing not even the slightest basics of statistical inference or causality.
- metiscus 6y ago
  I think that learning how to use a log table might cement certain relationships for more advanced students. But I do agree that in general there are probably better uses of one's time than to teach them as a first class citizen.
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veddox 6y ago
Our math teacher, a former engineer, once brought his slide rule to class when we were in grade 9. He posed a problem and raced us to the solution, slide rule vs. calculators. He beat us all...
markbnj 6y ago
My Dad, an engineer for GM/Cadillac, gave my brother and I each a slide rule back in the 60's. I remember marveling at the precision of it, and I did learn to use it for some calculations, but not to a level that impressed him :).
wykyee 6y ago
ssadada
ogogmad 6y ago
Also check out the quarter-square method and prosthaphaeresis.
watersb 6y ago
I love playing with slide rules because it wraps my brain into using logarithms everywhere. The game of Go also redecorates my thinking, in a way I cannot put into words. Slide rules!
supernova87a 6y ago
I think practice with a slide rule also gets you to sanity check your method and think whether the answer can be correct. Given how you could forget and inadvertently reverse the scales, etc, you have to think whether the answer you're getting makes sense by looking at the trend of the numbers. Plug and chug into a calculator takes some of that away.
sizzzzlerz 6y ago
Simply put, I love a slide rule. My dad gave me mine for my 17th birthday, 48 years ago and I’ve treasured it ever since. It’s the Pickett trig model and it served me well into my 3rd year of college as a EE. Its simple to use after you’ve been trained and totally reliable. It can also be quick as your skill using it develops. It sits in a drawer today but I take it out occasionally to play with. It truly is like a friend.
ashton314 6y ago
Oh this is wonderful. I first learned about slide rules from a math teacher back in junior high. I wasn't until a few years after that that my little sister gave me a slide rule for Christmas. \o/ After graduating high school I spent two years in Germany. Whenever I found a flea market or an antique store, I'd search for slide rules. I found two that were in pretty good condition. People always seemed a little confused as to why I wanted these. I guess they just didn't see the beauty in these simple, elegant devices.
lebski88 6y ago
I actually spent a bit of time learning about Slide Rules a few weeks ago as my Dad had put together a very cool interactive slide rule in JavaScript that I wanted to have a play with. https://adit.co.uk/sliderulev2.html https://adit.co.uk/sliderulev2.html One thing that struck me was that it does require a good instinct for the magnitude of numbers to use. Lots of fun though and surprisingly quick to use.
4x5-Guy 6y ago
Being in Junior College in 1973, some of the kids had 4 function calculators hanging off their belt. The rest of us in a tech track usually carried a slide rule. I did take a technical math class that involved programming a desktop calculator. Basically the first programming class I had. I wish I remembered what brand it was, I'd like to try to pick one up if I could find one.
throw0101a 6y ago
There's a 'Professor Herning' whose YouTube channel has both good tutorials on their use, as well as comparing many models (and the various scales they have): * https://www.youtube.com/c/ProfessorHerning/videos https://www.youtube.com/c/ProfessorHerning/videos

363 points by ngram 6y ago

surajs 6y ago

how eccentric! would much rather prefer a yt vid / tutorial pls.

TallGuyShort 6y ago
Such tutorials are readily findable by searching for "slide rule tutorial" on YouTube.
toolslive 6y ago
I think the preference is age related: Personally I prefer text over video, as I can process it at my speed, while with video I'm limited to the speed with which it's explained. My children all seem to prefer video.
- ghaff 6y ago
  You're almost certainly right. I hate searching for info on something that could be easily explained in a paragraph and maybe a screenshot and instead I have to watch through some video--usually with an ad. I confess that I really resist making videos of things unless I have no choice but I know a lot of people prefer them. A well-written and illustrated explanation like this one? I can't imagine preferring a video unless someone just wants some background noise and they don't really care about understanding the subject.
- JadeNB 6y ago
  > I think the preference is age related: Personally I prefer text over video, as I can process it at my speed, while with video I'm limited to the speed with which it's explained. > My children all seem to prefer video. When I ask for text transcripts of our training videos, in place of having to sit through 20 minutes of poorly acted out skits (that, re-certification being a periodic thing, I have sat through some 5 or 6 times already in my 10 years on the job), I am always told "but people enjoy the videos"—as if providing transcripts were somehow exclusive of providing videos.

bregma 6y ago

When I was in university, if you forgot your slide rule at an exam they kindly had a supply of log tables you could pick up from the proctor.

stblack 6y ago

One of the nicest things about a slide rule is, you can easily see the sensitivity of the result to variations of your last input. With a calculator, you get precision. With a slide rule, you get a value and its sensitivity.

KineticLensman 6y ago

Alas! No specific mention of the circular slide rule [0]. I have one in my desk drawer that I inherited from my dad - who used it in the 1970s to confirm his hip hacker credentials to his colleagues (they were building the control circuits for early radio-therapy machines in a cancer research institute). [0] https://americanhistory.si.edu/collections/object-groups/slide-rules/circular-slide-rules https://americanhistory.si.edu/collections/object-groups/sli...

analog31 6y ago
I was curious about circular slide rules, and found one on eBay for a few bucks, so what the heck. It turned out that it was a give-away from a company that used to be in my town, so I ended up having a nice conversation with the seller about his history with the company and so forth. He was a long retired engineer. Anyway, I started playing with ratios, and noticed that the thing is inaccurate! Further inspection and hypothesizing led me to discover that the scales were not printed concentrically with the mechanism. It's very slight, and not critical to my work in any way, so I treat it as part of the learning experience.
dan-robertson 6y ago
Circular slide rules tend to have smaller scales which may be harder to read but being circular has a great advantage. Look at how much effort in the OP is devoted to cases where the answer would ordinarily be off the end of the scale.
psim1 6y ago
Still very much in use: the E6B! https://en.wikipedia.org/wiki/E6B https://en.wikipedia.org/wiki/E6B
dctoedt 6y ago
My dad was a USAF fighter pilot; he kept his in-flight circular slide rule around for years. Unfortunately I didn't see it around when clearing out the house out after he and my mother died; I know I'd have kept it (because I've still got my yellow Pickett aluminum Model N-500-ES, © 1962).

derekp7 6y ago

One under-appreciated aspect of a slide rule, is for instantly seeing fraction reductions at a glance. For example, lets say I want to find out what aspect ratio a given screen resolution is at. I can set that resolution as a ratio on the slide rule's C/D scales (i.e., 1680x1050 becomes 1.68 one C, lined up with 1.05 on D. Then I glance over, and see immediately that is 16 x 10 resolution.) If the value goes off the scales, look up to the CF/DF scales. This is also great when you have a bunch of resistors and capacitors, and you need to build a circuit where the two are at a particular ratio. Set the ratio you want, then you can take whatever resistor you have, and see if you have a cap that is "close enough" to what you need.

KineticLensman 6y ago
> This is also great when you have a bunch of resistors and capacitors Yes! This is the sort of thing my Dad used them for (see my other comment here for the context)
kqr 6y ago
Also ratio multiplications, e.g. when increasing the amounts of ingredients in recipes to match a particular amount of something. So if the primary ingredient is chevre cheese, the recipe calls for 180 grams, but you can only buy it in 250 gram packages, you can set the slide rule to "180 over 250" and then just mechanically read off the proportionally correct amounts of all other ingredients. Slide rules are indispensable in the kitchen to me and I'm surprised they're not part of standard kitchen equipment like e.g. scales. Edit: Similarly, if the recipe is expressing ingredients in US units and you would want to know the international amounts, you can set the slide rule to the conversion ratio and again, mechanically read off the correct amounts as you go.
- gumby 6y ago
  This is one advantage of the customary (English language non-metric) units: the common ones are full of rational factors (1/2, 2/3 etc) — it’s pretty easy to adjust a recipe to the number of people.
myself248 6y ago

drfuchs 6y ago

Another great thing about slide rule days is that results are naturally constrained to 2 or 3 significant digits, so you'd never see nonsense like "The mountain is 10km high, or 32808.4ft" as if the 10km figure was accurate to 6 significant digits.

INGELRII 6y ago
Unnecessary accuracy is technical incompetence.
- ghaff 6y ago
  I think you mean precision in this case. If you're going to be all high and mighty you should probably get your facts correct.
sirsar 6y ago
I still remember the day I found out the "98.6 degrees" human body temperature was just an oversignificant conversion from "about 37 C, or maybe lower."
- JadeNB 6y ago
  > I still remember the day I found out the "98.6 degrees" human body temperature was just an oversignificant conversion from "about 37 C, or maybe lower." Really? According to Wikipedia, the Fahrenheit scale (https://en.wikipedia.org/wiki/Fahrenheit#History https://en.wikipedia.org/wiki/Fahrenheit#History) is about 18 years older than the Celsius scale (https://en.wikipedia.org/wiki/Celsius#History https://en.wikipedia.org/wiki/Celsius#History), and I'm surprised that human body temperature wasn't included as a calibration. (But of course the fact that I'm surprised by it doesn't mean it isn't true!)
  - _underfl0w_ 6y ago
    Could've sworn I remember hearing in grade school that one of then was actually calibrated with cow body temperatures. Don't remember which scale, though.

leetrout 6y ago

Circular slide rules are still used today in aviation in the form of the E6B flight computer. https://en.m.wikipedia.org/wiki/E6B https://en.m.wikipedia.org/wiki/E6B

ghaff 6y ago
Back when slide rules were still widely used and even after calculators had recently come in, you also saw a lot of industry-specific cardboard sliding scales that were basically slide rules with different types of units.

dave_aiello 6y ago

In an era marked by renewed interest in vinyl records, shouldn't there also be a corresponding interest in slide rules?

coldpie 6y ago
I dunno, man. I'm pretty well-versed in math and I find this page kind of baffling. I'm sure it's one of those things that is very easy to use once you learn it, but at least this introduction is very daunting. To do a basic multiplication (step 1 in the linked page) I need to use the C and D scales, each for two different purposes. Why not A and B? How do I remember it's C and D? Which part goes on C and which part goes on D? Then step 2 describes what to do if it goes off the edge of the scale, and it involves making an approximation. How do I know how accurate my approximation must be? Why is it to the tens digit? If I get larger numbers do I continue to use the tens digit, or some higher factor? We're only on step 2 and I'm already lost. This definitely looks like a great tool, and I'm kind of sad I don't have one or understand how it works, but this kind of complex learning and memorization up against dropping a needle on a record you like isn't really a great comparison.
- yuubi 6y ago
  It works better if you know how the scales are constructed and get familiar with properties of logarithms (mainly variations on log ab = log a + log b) C and D are plain log scales, where one decade is the length of the rule. They're sort of the default scales to use. Multiplication is commutative, so you put either number on either scale. The important thing is that the distance from the left index of the scale is proportional to the log of the number (reading the scale as 1 to 10), so you want to arrange the scales to add the lengths corresponding to your numbers such that the lengths add up. (Or so that you subtract the length of the divisor from the dividend, if you're dividing). You can get by without the approximation if you're willing to set up the multiplication, see that the product is out there in thin air, then move the slide to put the right index where you originally put the left index. (3 times 5: on the d scale find 3 and put the left index of the C scale there; opposite 5 on the C scale read nothing because there's no D scale there; try again using the right index of the C scale, which is the same thing as having another copy of the D scale out there to the right where the air was). A and B are each 2 copies of a log scale. You can absolutely use the left side of A and B for your numbers to multiply, and the product will always be on the scale. People normally use(d?) C and D because the precision is better and because the rest of the scales (like the trig and log-log) are constructed to work with them.

agumonkey 6y ago

Fascinating near invisible yet very high abstraction.

ghaff 6y ago

Slide rules to calculators was an incredibly fast technology transition for the sort of people who would have been using slide rules in the first place. A 5-function calculator was about $100 in 1974 (so about $350 in current dollars) and an HP scientific calculator was 3 or 4x as much. By about the next year, a TI scientific calculator was about the same and by a year or two later you could get an HP--which was the gold standard for about the same amount. And that was around the price point where making them not just OK to use but mandatory was reasonable at least in higher ed. I was one of the first classes in college where calculators were the norm and slide rules were maybe something you brought for backup at exams. (Calculators were still LEDs so you had to keep them charged.)

code4tee 6y ago

The “E6B Flight Computer” is a slide rule designed to perform various navigation calculations and is still a part of flight training for many pilots today. Once mastering it the old way student pilots are then allowed to use electronic versions or iPad apps that do all the calculations instantly.

lokedhs 6y ago

I'm of the generation that missed out on slide rules by a decade or so. My parents had one thta i played with as a kid, and I learned to do multiplicication and division with it. I'd like to get one now, mainly for fun, but if you want to buy one on Ebay in good condition, you have to pay quite a bit of money.

ghaff 6y ago
Plastic "student" slide rules are cheap on eBay. But, yes, quality K&E's etc. are expensive.
- lokedhs 6y ago
  Since this is something I want to keep on my desk, not only for decoration but for actually copute things if I'm bored, I really want tone of the nicer ones. It seems around 35 EUR is a normal price.
  - ghaff 6y ago
    Quality slide rules probably cost a lot more than that when they were still being manufactured :-)
- dwheeler 6y ago
  Quality K&E's were never cheap :-).
myself248 6y ago
Seems to me that this is also a lovely use for a desktop laser cutter. Dig out a copy of Pynomo or something and make your own scales that suit whatever specialty application you have in mind.
- 082349872349872 6y ago
  Came here to say nomograms are slide-rule-adjacent. https://en.wikipedia.org/wiki/Nomogram https://en.wikipedia.org/wiki/Nomogram

reaperducer 6y ago

I'm old enough that I had a slide rule when I was in school. Everyone did. They were built in to our pencil boxes. Most of us didn't use them, except the fancy-pantses who also insisted on using mechanical pencils. But we all knew how to use them. I'm graybeard enough that even through college, electric calculators were prohibited in class because they would give you answers without helping you understand the problem.

qrbLPHiKpiux 6y ago
> answers without helping you understand the problem This is my problem with common core math. It shows how to get to an answer, but I feel it bypasses fundamental understanding on why the answer is what it is.
- metiscus 6y ago
  I feel that common core focuses more on teaching the various methods than embracing the idea that correct answers and understanding are largely what matter rather than any specific method.
  - ghaff 6y ago
    That's hardly a new thing with common core. See Tom Lehrer's "The New Math." "...But in the new approach, As you know, the important thing is to understand what you're doing, Rather than to get the right answer."
    - metiscus 6y ago
      Interestingly that song is apparently about the first time they tried to massively redesign the mathematics curriculum based on on fuzzy math that we were falling behind the Soviets or whatever. My parents tell me they rebased around set theory early etc but it foundered on nearly the same rocks that common core mathematics is now - teacher must be well educated in the pedagogical paradigm and fully understand it. E.g. you can't just take the same set of teachers from math v1.2.1 and slam them into math v2.1.0 or whatever without significant issues the two approaches are not abi compatible. That's why in my with opinion common core we are seeing teachers test finding answers via method 1 specifically or method 2 specifically rather than encouraging the use of either to get a correct answer by an understood method. /rant

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wdb 6y ago

Cool, now I finally know how to use this rule that I got when me and my siblings were clearing up the family house after my parents passed away. It's really fascinating, I will show my nephews when I am back in the home country :) Thanks for posting!

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vilesolid 6y ago

See the 18 proven ways on how to make 10 dollars a day online (2020)? https://vilesolid.com/how-to-make-10-dollars-a-day/ https://vilesolid.com/how-to-make-10-dollars-a-day/

ColinWright 6y ago

A few years ago I met Fred Haise Jr and got him to sign one of my Slide Rules. He was so excited to see it, took it from me, and started to show the event host how to use it! He asked me what I use to lubricate it, and when I said "Pencil graphite" he got even more excited. Apparently a lot of the other astronauts had used fancy light lubrication oils, but he always used a pencil and never had any problems. He was a lovely man, and it was fabulous to enthuse with him over this wonderful piece of technology.

mcguire 6y ago
Powdered graphite is an excellent lubricant that doesn't attract crud. My father had a little squeeze tube of it for locks; it eventually ran out and I haven't seen any more since.
- philiplu 6y ago
  You can find the small tubes at hobby stores, with the supplies for Pinewood Derby cars for Cub Scouts. I went through several tubes during my son's years in Scouts.
  - avhon1 6y ago
    You can also get it at hardware stores for lubricating locks.
    - EricE 6y ago
      The versions for lubricating motorcycle cables are finer and less messy than the cheap stuff they sell for locks. If you want to be neater with your slide rule, anyway :)

philiplu 6y ago

What a blast from the past. I can draw a direct line from my encountering a slide rule to ending up as a programmer. I owe my career to that device. I was a nerdy 10 year old kid who liked doing arithmetic in 1970, but didn't know anything particularly advanced. I convinced my parents to get me a slide rule as a Christmas present that year; a basic white Post model 1447 - I know that because I'm looking at it right now. It's been in my desk drawer forever as I could never convince myself to throw it away, even though I've long since lost the sliding cursor. Anyway, I got the slide rule, had fun with basic multiplication/division, but didn't understand what the S, T, and L scales on the back were for. Sine/Tangent/Logarithm? What are those? Off to the library, where I picked up a Tutor-Text book [0] on trigonometry, discovered I'd better first learn some algebra, picked up another Tutor-Text book on that, and began a two-year tear teaching myself algebra to integral calculus. Which meant I tested out of a couple years of math in high school, ran out of courses to take, and in my junior year was allowed to walk to the local college to take 2nd year Calc classes. At that college, they started letting me play with the computers, both an IBM 5100 APL machine over one summer, and hands-on access to the IBM 11/30 clone minicomputer that was the main machine. The math prof pointed me at Knuth's "The Art of Computer Programming", and that began my transition from pure mathematics to computer programming/science instead. I even wrote a MIXAL assembler/MIX simulator for the minicomputer that the college ended up using to teach an assembly language course. So thank you, Post, Pickett, K&E! And Tutor-Text as well. [0]: https://gamebooks.org/Series/457/Show https://gamebooks.org/Series/457/Show

ezequiel-garzon 6y ago
Thanks for sharing such a wonderful story. Something tells me your career path wouldn’t have changed significantly if you had never touched a slide rule, though :)
neilpanchal 6y ago
> So thank you, Post, Pickett, K&E! And Tutor-Text as well. I didn't even grow up in this era and I keep buying stuff from eBay purely out of fascination for old ways of doing things. These names on all kinds of things I have horded - architectural templates, drafting machine, cutting mat, compass set, lettering templates, etc. Thanks for sharing your story!

Bloggerzune 6y ago

A well-written and illustrated explanation like this one? I can't imagine preferring a video unless someone just wants some background noise and they don't really care about understanding the subject. https://www.bloggerzune.com/2019/10/a-bloggers-big-mistakes-part-2-blogger.html https://www.bloggerzune.com/2019/10/a-bloggers-big-mistakes-...

tzs 6y ago

One unexpected advantage in some circumstances of a slide rule over current portable computing devices is that it does not have memory. You are allowed to bring a calculator to ham radio license exams in the US, but you have to clear its memory (both data and program memory for programmable calculators) first. If the examiners aren't sure you have done so, they are supposed to disallow the calculator. Unlike many other standardized tests, there is no specific list of what calculators are allowed. I brought my HP-15C, but wasn't sure that the examiners would be familiar with it and so wasn't sure I'd be able to convince them that I had cleared it. I also brought a slide rule. That way if the examiners disallowed my HP-15C I'd still be covered. They did allow the HP-15C, and it turned out that even though I took all three exams (Technician, General, and Extra) that day, I only actually used the calculator once. The questions are all multiple choice, and there was only one where a quick mental approximation wasn't enough to identify the right answer.

Someone 6y ago
Nitpick: a slide rule does have memory, but it is small and gets cleared when doing computations. One typically can store one number by moving the slide and another one by location of the cursor. It also is fairly hard to hide the fact that the memory isn’t cleared. Many slide rules also have some read-only memory, for example ’storing’ the constant π.

ssimpson 6y ago

I've been trying to figure out how to use my grandfathers Dietzgen Maniphase Multiplex Decimal Trigtype Log Log rule. I found the manual on this site! Very cool!

dylan604 6y ago

One of my favorite scenes in "Apollo 13" has a CO2 hazy Jim Lovell asking Houston to double check his math, and it cuts to a room full of engineers as they all grab their slide rules to calculate the answers Jim had just done in his head/scratch pad.

xenocyon 6y ago

As someone who grew up in India in the 20th century: slide rules are unfamiliar, but we used log tables (calculators of any kind were prohibited through high school and standardized tests). For those unfamiliar, log tables serve to replace multiplication/division of floating-point numbers with addition/subtraction instead, making scientific computation a lot easier. The main benefit of introducing this friction, rather than allowing calculators, is that it (a) encourages one to do simple calculations by hand, and (b) gets one in the habit of quickly double checking that log-table-based results fall in the correct ballpark. Calculators induce a sort of mindlessness where glaring orders-of-magnitude errors pass us by since we expect the machine to get it right. With all that said, I don't know that I would recommend the use of log tables to high schoolers in the 21st century. That effort might be better utilized on more pressing needs e.g. statistical literacy. Many folks (including me) got entirely through STEM-focused high school knowing not even the slightest basics of statistical inference or causality.

metiscus 6y ago
I think that learning how to use a log table might cement certain relationships for more advanced students. But I do agree that in general there are probably better uses of one's time than to teach them as a first class citizen.

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veddox 6y ago

Our math teacher, a former engineer, once brought his slide rule to class when we were in grade 9. He posed a problem and raced us to the solution, slide rule vs. calculators. He beat us all...

markbnj 6y ago

My Dad, an engineer for GM/Cadillac, gave my brother and I each a slide rule back in the 60's. I remember marveling at the precision of it, and I did learn to use it for some calculations, but not to a level that impressed him :).

wykyee 6y ago

ssadada

ogogmad 6y ago

Also check out the quarter-square method and prosthaphaeresis.

watersb 6y ago

I love playing with slide rules because it wraps my brain into using logarithms everywhere. The game of Go also redecorates my thinking, in a way I cannot put into words. Slide rules!

supernova87a 6y ago

I think practice with a slide rule also gets you to sanity check your method and think whether the answer can be correct. Given how you could forget and inadvertently reverse the scales, etc, you have to think whether the answer you're getting makes sense by looking at the trend of the numbers. Plug and chug into a calculator takes some of that away.

sizzzzlerz 6y ago

Simply put, I love a slide rule. My dad gave me mine for my 17th birthday, 48 years ago and I’ve treasured it ever since. It’s the Pickett trig model and it served me well into my 3rd year of college as a EE. Its simple to use after you’ve been trained and totally reliable. It can also be quick as your skill using it develops. It sits in a drawer today but I take it out occasionally to play with. It truly is like a friend.

ashton314 6y ago

Oh this is wonderful. I first learned about slide rules from a math teacher back in junior high. I wasn't until a few years after that that my little sister gave me a slide rule for Christmas. \o/ After graduating high school I spent two years in Germany. Whenever I found a flea market or an antique store, I'd search for slide rules. I found two that were in pretty good condition. People always seemed a little confused as to why I wanted these. I guess they just didn't see the beauty in these simple, elegant devices.

lebski88 6y ago

I actually spent a bit of time learning about Slide Rules a few weeks ago as my Dad had put together a very cool interactive slide rule in JavaScript that I wanted to have a play with. https://adit.co.uk/sliderulev2.html https://adit.co.uk/sliderulev2.html One thing that struck me was that it does require a good instinct for the magnitude of numbers to use. Lots of fun though and surprisingly quick to use.

4x5-Guy 6y ago

Being in Junior College in 1973, some of the kids had 4 function calculators hanging off their belt. The rest of us in a tech track usually carried a slide rule. I did take a technical math class that involved programming a desktop calculator. Basically the first programming class I had. I wish I remembered what brand it was, I'd like to try to pick one up if I could find one.

throw0101a 6y ago

There's a 'Professor Herning' whose YouTube channel has both good tutorials on their use, as well as comparing many models (and the various scales they have): * https://www.youtube.com/c/ProfessorHerning/videos https://www.youtube.com/c/ProfessorHerning/videos