10 ms·

Why a Slide Rule Works

105 points by zdw 5y ago

hilbert42 5y ago
I'm not commenting on this story and here's why (it's a copy of my feedback to that web site): "I have not yet read this article because it's too difficult to read. Even the text I'm entering into this comment box is almost illegible. I have to doublely check to see what I've written. Presumably the reason you've chosen a gray text which to me on my smartphone looks to have no more than 20% saturation together with a fine spindle like font is that it looks artistic on your hi-res, high dynamic range monitor but it's essentially illegible on my smartphone (1080x1920px). I'm not the only one who is complaining, many have whinged about very feint essentially illegible text on the web - it's a common complaint yet illegible websites like yours still persist. Presumably, I could copy and paste the text into a text editor to read it but then I'd lose the images. It's messy and I shouldn't have to do it. That said, the images of the slide rule are quite readable. BTW, I'm not some casual narky reader who's being critical for the sake of it. I am a regular slide rule user. In fact, I'm looking at my two slide rules on my desk now - one's a Hemmi Darmstadt No 130 and the other is a Faber Castell No 2/83 N. The Hemmi was from my student days (before calculators), and the F/Castell is about 60 years old and belonged to my father who was an engineer. Both rules are still highly usable."
- willcipriano 5y ago
  Are you running a dark mode plugin or something? It works fine for me.
  - hilbert42 5y ago
    Absolutely not, this phone is stock standard Huawei Honor (GR5) 2017 It's completely untweaked (unlike most of my rooted phones). In fact, I use this phone as a workhorse because the screen is very good for a cheap phone. (Even if we hate Huawei, we have to admit the quality of its stuff is pretty good.) It'd be interesting to know what you are using. As soon as I post this I'll fire up the PC and see how it looks there. I'll let you know.
  - hilbert42 5y ago
    Update: See my reply to dahardt. Reckon the problem's (mostly) solved. Thanks for your comment.
- dahart 5y ago
  You might mention which device & browser. I don’t see any issues at all on an iPhone nor desktop. Could it be a bug in your setup, and not something the site has much control over?
  - hilbert42 5y ago
    See reply to willipriano. Browser Chrome. As I said, I'll try my PC and get back. At this point, all I can say is that everything else I've looked at on HN in the last several is perfect. ...Thinking, if OK with you this could be a typeface (font substitution) problem. If so, it ought to show up on the PC as the typefaces are mostly different.
    - deleted 5y ago
      [deleted]
  - hilbert42 5y ago
    OK, I'm now on the PC. My main PC with the hi-res monitor is being refurbished so this 2nd PC will have to do, it only has an old Dell E228WFP monitor (1680x1050) attached. The browser is now Firefox. This is a Windows PC with the browser font set to its default size. The webpage is now readable but it's still low in intensity (contrast) and the MS ClearType is having considerable difficulty in keeping certain characters sharp—in fact it's hardly working—the 'i' 'l' and 'm' look annoyingly fuzzy. When I increase the font (CTRL +) several sizes in the browser it improves out of sight and the text becomes completely and easily readable. It's a shame I can't post some screen shots to show how significantly different that typeface is under different viewing environments/conditions. It only proves the point that web designers shouldn't just take what they see on their own monitors and assume it's the same as everyone else sees it. As mentioned, I'm not alone in complaining about low contrast grayish typefaces, here's the first other complaints I've just found: https://www.wired.com/2016/10/how-the-web-became-unreadable/ https://www.wired.com/2016/10/how-the-web-became-unreadable/ https://www.contrastrebellion.com/#page2 https://www.contrastrebellion.com/#page2 Incidentally, an interesting observation is that the character pi, π, in the webpage is perfectly viewable on the smartphone and has good contrast. Clearly it's from a different typeface set, it also proves that the text's typeface is the culprit in that it doesn't view well on all displays. I'll now go back to the smartphone and figure out what typeface the phone is displaying the text in. Thanks for your comment.
- khedoros1 5y ago
  On both my desktop (Linux+Firefox @1440p) and phone (Android+Firefox @2160x1080), the text is black on a white background, in a reasonably-legible font, and at a reasonable size. Trying it in Chrome doesn't look significantly different on either device.
  - buescher 5y ago
    It doesn't work on my K&E or my Pickett either.
    - hilbert42 5y ago
      As I've said to several other posters, I reckon it's a font substitution problem - some fonts display much better than others in certain environments. BTW, an interesting observation, when I first posted the comment it was up-voted, it's now been down-voted to just below where it started. I think this proves the point that not everyone is viewing that page with equal ease.
dahart 5y ago
Must be in the air, I just watched a YouTube recommended vid by Mathologer on the circular slide rule that was interesting. https://youtu.be/ZIQQvxSXLhI https://youtu.be/ZIQQvxSXLhI
- szszrk 5y ago
  I love that it's still used in watches. Some brands have it build into watches bezel, with some predefined marks for popular conversions like galons/liters, miles/nautical miles/kilometers and so on. It looks fun and is fun. Of course the rule itself is very limited as you basically have to figure out where is the decimal point by yourself (even for small numbers) but it's actually very precise and may be useful with practice. Below some examples that are not very expensive [1], also a Casio manual [3] I found very helpful and visually appealing. [1] Seiko SSC632, Seiko SRPB59J1, Casio EF527D-1AV [2] https://support.casio.com/answer.php?rgn=4&cid=002001009001&qid=24394&num=1 https://support.casio.com/answer.php?rgn=4&cid=002001009001&...
- function_seven 5y ago
  Definitely in the air. I just watched that video last week and was blown away by the rubber band analogy. So simple and intuitive what's happening as the wheel takes up the infinitely-stretching rubber band. I always thought I understood logarithms—and I actually did somewhat—but that visual really drove home the "continuous ratio-ing" that's happening as the scale is built.
- perilunar 5y ago
  > Must be in the air Ha. The famous E6B flight computer is a circular slide rule. Edit: it's mentioned in the video.
dragontamer 5y ago
So I've known about slide-rules for a while. What I didn't realize was that the mechanical principles of slide-rules were applied to fire-control computers on WW2-era Battleships. https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer These computers had slide-rule like cylinders that would rotate. As you aimed the gun sights "at" a target, the gun's coordinates were being mapped to a cylinder, which would move the gun a different direction (you have to aim the gun "higher" the further away the target is, to account for gravity "drooping" the bullet). In effect; the weirdly shaped cylinder inside the fire-control computer is a pre-computed solution that maps x/y coordinate inputs to a z-coordinate output (where "z" would be fed into the gun's raw aiming system). The different parameters of the gun were programmed in with gears and cranks, moving the cylinder around physically. For more details, see: https://www.youtube.com/watch?v=gwf5mAlI7Ug https://www.youtube.com/watch?v=gwf5mAlI7Ug Its a 20-minute video. The cylinder mechanism (of 2x inputs mapped to 1x output) is specifically talked about here: https://youtu.be/gwf5mAlI7Ug?t=636 https://youtu.be/gwf5mAlI7Ug?t=636 . Carefully crafted cylinders could be any pre-computed 2-input / 1-output function. --------- Mechanical computers are fun. Slide rules are but the simplest kind. People were using more complicated "mechanical computers" for very serious combat / rangefinding / etc. systems just a few decades ago, before the advent of modern digital computers.
- 7thaccount 5y ago
  Mechanical computers are really cool. Veritasium just did a 2 part video on them. The second goes over some ML applications for the future. You can make a really tiny and energy efficient mechanical chip to do some cool things.
  - HideousKojima 5y ago
    Technically Veritasium's videos were about analog computers (of which some mechanical computers are a subset, it's entirely possible to make a digital mechanical computer though it would be extremely slow).
    - 5y ago
derekp7 5y ago
There are some things that a slide rule is superior for -- one item I can think of is visualizing an arbitrary range of fractional values. For example, lets say you need a capacitor and a resistor with values in a particular ratio. Any pair will work in your given circuit (within reason), as long as that ratio is maintained. You have a drawer full of various resistors and another of capacitors, and need to find a pair that will work. So you set your slide rule to that fraction (let's say 1.7 / 3.3), and you can then pull up any resistor and determine which size capacitor can be used by glancing at the slide rule. (Of course you still have to keep track of the magnitudes in your head, but being in the habit of that makes you a better engineer anyway).
- hilbert42 5y ago
  "There are some things that a slide rule is superior for -- one item I can think of is visualizing an arbitrary range of fractional values." Exactly, similar to the way log scales make visualizing a range of results across the slide rule no matter what one is doing. Similarly, I have a number of good digital multimeters but I also keep several analog AVO meters, https://en.wikipedia.org/wiki/Avometer https://en.wikipedia.org/wiki/Avometer, to give me a sense of proportion if I'm adjusting something (nulling a discriminator etc.).
- JKCalhoun 5y ago
  I implemented Ohm's Law as you describe for an iOS App some years back [1]. Tried also to figure out how to do it in Javascript (still learning, love it if someone could really make it nice for the rest of us to use) [2]. [1] Perfboard (5th screenshot shows it): https://apps.apple.com/us/app/perfboard/id46595187 https://apps.apple.com/us/app/perfboard/id46595187 [2] SlideRule.js: https://github.com/EngineersNeedArt/SlideRule https://github.com/EngineersNeedArt/SlideRule
zabzonk 5y ago
When I was in school in the late 60s a slide-rule company gave a special offer to us, which all of our parents (wanting us to succeed in the bright technological future) duly bought into. As far as I know, none of us ever actually used them, preferring paper log tables. We were also taught how to use mechanical adding machines, possibly the last people to be lumbered with this information, which mercifully I have completely forgotten.
- xyzzy21 5y ago
  I was probably the last generation in the US in the 1970s to willingly learn slide rules - the HP-35 had been out a few years and new scientific calculators already made the demise of slide rules pretty obvious to even us nerdlets. One of my prized inheritances from my engineer father is his slide rule (complete with leather case).
  - killjoywashere 5y ago
    I have a few slide rules at this point, including a Hemmi 200 "Made in Occupied Japan" https://www.sliderulemuseum.com/Hemmi.htm https://www.sliderulemuseum.com/Hemmi.htm
    - hilbert42 5y ago
      Thanks for the link. I've just seen my Sun Hemmi No. 130 System Darmstadt (which I'm looking at now and that I mentioned in my earlier post). It's still in excellent condition except the glass in the cursor has a crack in it).
  - astangl 5y ago
    In our high school physics class in early 80s, the teacher didn't care for calculators, so you'd have to do your calculations by hand, or learn to use a slide rule. I learned to use a slide rule, along with a buddy. I don't remember others in the class using slide rules, but looking back now, I have a hard time believing everybody else used pencil & paper. So there were probably others. I think that teacher didn't retire for another 20 years, so he may have had kids in the 21st century still learning to use slide rules for his class.
xyzzy21 5y ago
Mathologer has a nice video about this via "log wheels". https://www.youtube.com/watch?v=ZIQQvxSXLhI https://www.youtube.com/watch?v=ZIQQvxSXLhI
albert_e 5y ago
For those who prefer this concept explained to you with a video and examples -- https://www.youtube.com/watch?v=waiprjueVpQ https://www.youtube.com/watch?v=waiprjueVpQ
jhallenworld 5y ago
A nice casual use case for a slide rule is metric conversion: https://americanhistory.si.edu/collections/search/object/nmah_1215014#:~:text=This%20ten%2Dinch%2C%20one%2D,of%20metric%20and%20conventional%20units https://americanhistory.si.edu/collections/search/object/nma.... Consider that this slide is doing two things for you: it remembers the conversion factor (for a bunch of difference conversions), and it does the multiplication or division.
- ddingus 5y ago
  I want one of these. Right now, I do this conversion a lot more than usual. Over time, I have mapped many of my familiar Imperial unit touchstone type references onto Standard International units, so I am largely good to go, but this would have been very useful during the process. And what I mean here is just ones sense of scale and ability to mentally estimate and work with familiar ratios to arrive at solid first order approximations. These are important, in that one can set expectations about the answer quickly and accurately. Doing that is a great check on the problem overall and or makes mental analysis quick and robust. It is all the little things, like a sheet of paper being 0.004" or 0.1mm. Looking at something, say to understand whether it can be manufactured, or maybe features are too small or large and fall outside process limits. Or, given a force, something happening, or one suspects may have happened, working backward to arrive at root cause of failure, having that kind of info "in head", useable directly in that internal way, knowing how it might appear, feel, be seen, sound like, is high value. Tools like this really help with all that. Combining the data with motions, the slide, how far, etc all build robust mental connections. It just starts happening. For me at least, I just begin to "know" whether it make sense, will fit, break, etc...
  - spc476 5y ago
    I have four slide rulers, and all of them I picked up at various antique shops. The latest one I bought is the same type that the Apollo astronauts took to the moon (Picket N600-ES, about 6" (15.5cm) long). I paid about US$5 for it.
    - 5y ago
bediger4000 5y ago
I tried to find a place to buy a new slide rule for my 15-year old. I've got twins in different schools, one school doing a lot more math than the other, and I wanted to get him going on logarithms. Couldn't find a new one, just antiques on ebay, etc. I ended up making one of the paper ones, but they're not the same. Does anybody make new slide rules?
- HappyJoy 5y ago
  Maybe an E6B would be helpful.
- floren 5y ago
  I don't think anyone still makes new slide rules, except for the E6B flight computer which is rather specialized. However, you should be able to get a metal Pickett slide rule on ebay for a reasonable price; they're great slide rules and being metal rather than wood will tend to hold up better over the years (moisture can really mess up a wood slide rule). Something like this: https://www.ebay.com/itm/234503446574 https://www.ebay.com/itm/234503446574
  - perilunar 5y ago
    > except for the E6B flight computer which is rather specialized That's a positive, not a negative, since it demonstrates a whole host of practical problems that can be solved quickly with a slide rule. And they still work fine for general multiplication, and they are cheap and easy to get.
- derekp7 5y ago
  You can buy refurbished and also new-in-box (a bit expensive depending on the model) slide rules from various sites, such as https://www.sphere.bc.ca/test/sruniverse.html https://www.sphere.bc.ca/test/sruniverse.html. I thought about getting into hand making them, figured out most of the techniques that I can do in my garage with some components (the end brackets, and cursor runners) being made on a 3D printer. But I'm hung up on where to get the cursor springs from, or what would be a good substitute. One of these days I may revisit the topic.
- 5y ago
jhallenworld 5y ago
For old calculating machines I want to recommend Prof. Chris Staecker's YouTube channel, his videos are enjoyable. Here is a play-list: https://www.youtube.com/watch?v=swCy6pQSEpk&list=PLLFpXNanTP9X6lHrX9qoJroqGAQRDDvV9 https://www.youtube.com/watch?v=swCy6pQSEpk&list=PLLFpXNanTP... Inspired me to buy a Comptometer: https://en.wikipedia.org/wiki/Comptometer https://en.wikipedia.org/wiki/Comptometer If all you need to do is add, Comptometers are the fastest machines so far invented. They are fast because you can enter entire numbers at once (as a "chord" with multiple fingers pressing multiple digits at once). No need to hit "+" key or pull a lever between numbers, each button press is an immediate addition. I'm thinking of making an electronic version- it would have the same Comptometer key layout, but have more operations (for example, hold multiply "shift" key down while entering number for a multiply).
- pwr-electronics 5y ago
  For graphical computation, I recommend Nomographer's YouTube channel https://www.youtube.com/channel/UCOLYtsL4ge6QfaAvBDeG1IA https://www.youtube.com/channel/UCOLYtsL4ge6QfaAvBDeG1IA
pkaye 5y ago
I think these are essentially nomograms. I seem to recall in college engineering back in 90s they taught us how to design nomograms for simple functions.
zanethomas 5y ago
That's what I had for a calculator in chemistry.
goache 5y ago
I recently created a web comic explaining slide rules! https://randomlyunique.com/plancky/2021/slide-rules/index.html https://randomlyunique.com/plancky/2021/slide-rules/index.ht...
- ASalazarMX 5y ago
  You comic is great, do you have an official RSS feed?
  - goache 5y ago
    Oh wow - thanks for the compliment :-) https://randomlyunique.com/feeds/all.atom.xml https://randomlyunique.com/feeds/all.atom.xml
marcodiego 5y ago
I asked this once. The answer I got was: because "Log(x) + Log(y) = Log(XY), and the scales of a slide rule are logarithmic."
s0teri0s 5y ago
I love slide rules. I'm old enough to have had one with a belt case that I brought to school. But I have to ask, what is wrong with a ridiculous amount of precision?
GeorgeTirebiter 5y ago
https://www.sliderulemuseum.com/Manuals/M220_AnEasyIntroductionToTheSlideRule_IsaacAsimov_1965.pdf https://www.sliderulemuseum.com/Manuals/M220_AnEasyIntroduct... is the best book ever for a beginning slide rule user.
evilotto 5y ago
The ark lands after The Flood. Noah lets all the animals out. Says, "Go and multiply." Several months pass. Noah decides to check up on the animals. All are doing fine except a pair of snakes. "What's the problem?" says Noah. "Cut down some trees and let us live there", say the snakes. Noah follows their advice. Several more weeks pass. Noah checks on the snakes again. Lots of little snakes, everybody is happy. Noah asks, "Want to tell me how the trees helped?" "Certainly", say the snakes. "We're adders, and we need logs to multiply."
- vincent-manis 5y ago
  This reminds me of the cartoon diagram of a computer posted in our university's IBM 7044 computer room circa 1968. I've forgotten most of it, but I still remember the snake swimming in a little pool of water, subtitled “Floating-point adder”.
zwieback 5y ago
My sister is 3 years older and she still learned slide rule in high school but I didn't. Being a nerd I had my dad teach me though. One of the key things is just the right amount of grease in the tracks.
agumonkey 5y ago
I find this to be the most abstract yet primitive computing device. Bands and marks and you hop right into logarithmic relationships.
tedunangst 5y ago
> Notice that the 1 of the bottom is under π on the top bar. I spent a long time staring at the picture until I figured out the bottom is the second row, and there are four rows of numbers below the bottom.
throw0101a 5y ago
A comment from a previous discussion: --- The Professor Herning YT channel has a bunch of videos on both using slide rules and reviews/comparisons of various ones: * https://www.youtube.com/c/ProfessorHerning/videos https://www.youtube.com/c/ProfessorHerning/videos The "Practical Slide Rule" [0] and "Basic slide rule theory and use" [1] playlists are a good intro: [0] https://www.youtube.com/playlist?list=PL_qcL_RF-Zyu6ugp3E2nB9xoTSwpy1G-F https://www.youtube.com/playlist?list=PL_qcL_RF-Zyu6ugp3E2nB... [1] https://www.youtube.com/playlist?list=PL_qcL_RF-ZyvJYtIr9NRXJX958d6BgdbN https://www.youtube.com/playlist?list=PL_qcL_RF-ZyvJYtIr9NRX... --- https://news.ycombinator.com/item?id=30971066 https://news.ycombinator.com/item?id=30971066

105 points by zdw 5y ago

I'm not commenting on this story and here's why (it's a copy of my feedback to that web site): "I have not yet read this article because it's too difficult to read. Even the text I'm entering into this comment box is almost illegible. I have to doublely check to see what I've written. Presumably the reason you've chosen a gray text which to me on my smartphone looks to have no more than 20% saturation together with a fine spindle like font is that it looks artistic on your hi-res, high dynamic range monitor but it's essentially illegible on my smartphone (1080x1920px). I'm not the only one who is complaining, many have whinged about very feint essentially illegible text on the web - it's a common complaint yet illegible websites like yours still persist. Presumably, I could copy and paste the text into a text editor to read it but then I'd lose the images. It's messy and I shouldn't have to do it. That said, the images of the slide rule are quite readable. BTW, I'm not some casual narky reader who's being critical for the sake of it. I am a regular slide rule user. In fact, I'm looking at my two slide rules on my desk now - one's a Hemmi Darmstadt No 130 and the other is a Faber Castell No 2/83 N. The Hemmi was from my student days (before calculators), and the F/Castell is about 60 years old and belonged to my father who was an engineer. Both rules are still highly usable."

willcipriano 5y ago
Are you running a dark mode plugin or something? It works fine for me.
- hilbert42 5y ago
  Absolutely not, this phone is stock standard Huawei Honor (GR5) 2017 It's completely untweaked (unlike most of my rooted phones). In fact, I use this phone as a workhorse because the screen is very good for a cheap phone. (Even if we hate Huawei, we have to admit the quality of its stuff is pretty good.) It'd be interesting to know what you are using. As soon as I post this I'll fire up the PC and see how it looks there. I'll let you know.
- hilbert42 5y ago
  Update: See my reply to dahardt. Reckon the problem's (mostly) solved. Thanks for your comment.
dahart 5y ago
You might mention which device & browser. I don’t see any issues at all on an iPhone nor desktop. Could it be a bug in your setup, and not something the site has much control over?
- hilbert42 5y ago
  See reply to willipriano. Browser Chrome. As I said, I'll try my PC and get back. At this point, all I can say is that everything else I've looked at on HN in the last several is perfect. ...Thinking, if OK with you this could be a typeface (font substitution) problem. If so, it ought to show up on the PC as the typefaces are mostly different.
  - deleted 5y ago
    [deleted]
- hilbert42 5y ago
  OK, I'm now on the PC. My main PC with the hi-res monitor is being refurbished so this 2nd PC will have to do, it only has an old Dell E228WFP monitor (1680x1050) attached. The browser is now Firefox. This is a Windows PC with the browser font set to its default size. The webpage is now readable but it's still low in intensity (contrast) and the MS ClearType is having considerable difficulty in keeping certain characters sharp—in fact it's hardly working—the 'i' 'l' and 'm' look annoyingly fuzzy. When I increase the font (CTRL +) several sizes in the browser it improves out of sight and the text becomes completely and easily readable. It's a shame I can't post some screen shots to show how significantly different that typeface is under different viewing environments/conditions. It only proves the point that web designers shouldn't just take what they see on their own monitors and assume it's the same as everyone else sees it. As mentioned, I'm not alone in complaining about low contrast grayish typefaces, here's the first other complaints I've just found: https://www.wired.com/2016/10/how-the-web-became-unreadable/ https://www.wired.com/2016/10/how-the-web-became-unreadable/ https://www.contrastrebellion.com/#page2 https://www.contrastrebellion.com/#page2 Incidentally, an interesting observation is that the character pi, π, in the webpage is perfectly viewable on the smartphone and has good contrast. Clearly it's from a different typeface set, it also proves that the text's typeface is the culprit in that it doesn't view well on all displays. I'll now go back to the smartphone and figure out what typeface the phone is displaying the text in. Thanks for your comment.
khedoros1 5y ago
On both my desktop (Linux+Firefox @1440p) and phone (Android+Firefox @2160x1080), the text is black on a white background, in a reasonably-legible font, and at a reasonable size. Trying it in Chrome doesn't look significantly different on either device.
- buescher 5y ago
  It doesn't work on my K&E or my Pickett either.
  - hilbert42 5y ago
    As I've said to several other posters, I reckon it's a font substitution problem - some fonts display much better than others in certain environments. BTW, an interesting observation, when I first posted the comment it was up-voted, it's now been down-voted to just below where it started. I think this proves the point that not everyone is viewing that page with equal ease.

dahart 5y ago

Must be in the air, I just watched a YouTube recommended vid by Mathologer on the circular slide rule that was interesting. https://youtu.be/ZIQQvxSXLhI https://youtu.be/ZIQQvxSXLhI

szszrk 5y ago
I love that it's still used in watches. Some brands have it build into watches bezel, with some predefined marks for popular conversions like galons/liters, miles/nautical miles/kilometers and so on. It looks fun and is fun. Of course the rule itself is very limited as you basically have to figure out where is the decimal point by yourself (even for small numbers) but it's actually very precise and may be useful with practice. Below some examples that are not very expensive [1], also a Casio manual [3] I found very helpful and visually appealing. [1] Seiko SSC632, Seiko SRPB59J1, Casio EF527D-1AV [2] https://support.casio.com/answer.php?rgn=4&cid=002001009001&qid=24394&num=1 https://support.casio.com/answer.php?rgn=4&cid=002001009001&...
function_seven 5y ago
Definitely in the air. I just watched that video last week and was blown away by the rubber band analogy. So simple and intuitive what's happening as the wheel takes up the infinitely-stretching rubber band. I always thought I understood logarithms—and I actually did somewhat—but that visual really drove home the "continuous ratio-ing" that's happening as the scale is built.
perilunar 5y ago
> Must be in the air Ha. The famous E6B flight computer is a circular slide rule. Edit: it's mentioned in the video.

dragontamer 5y ago

So I've known about slide-rules for a while. What I didn't realize was that the mechanical principles of slide-rules were applied to fire-control computers on WW2-era Battleships. https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer https://en.wikipedia.org/wiki/Mark_I_Fire_Control_Computer These computers had slide-rule like cylinders that would rotate. As you aimed the gun sights "at" a target, the gun's coordinates were being mapped to a cylinder, which would move the gun a different direction (you have to aim the gun "higher" the further away the target is, to account for gravity "drooping" the bullet). In effect; the weirdly shaped cylinder inside the fire-control computer is a pre-computed solution that maps x/y coordinate inputs to a z-coordinate output (where "z" would be fed into the gun's raw aiming system). The different parameters of the gun were programmed in with gears and cranks, moving the cylinder around physically. For more details, see: https://www.youtube.com/watch?v=gwf5mAlI7Ug https://www.youtube.com/watch?v=gwf5mAlI7Ug Its a 20-minute video. The cylinder mechanism (of 2x inputs mapped to 1x output) is specifically talked about here: https://youtu.be/gwf5mAlI7Ug?t=636 https://youtu.be/gwf5mAlI7Ug?t=636 . Carefully crafted cylinders could be any pre-computed 2-input / 1-output function. --------- Mechanical computers are fun. Slide rules are but the simplest kind. People were using more complicated "mechanical computers" for very serious combat / rangefinding / etc. systems just a few decades ago, before the advent of modern digital computers.

7thaccount 5y ago
Mechanical computers are really cool. Veritasium just did a 2 part video on them. The second goes over some ML applications for the future. You can make a really tiny and energy efficient mechanical chip to do some cool things.
- HideousKojima 5y ago
  Technically Veritasium's videos were about analog computers (of which some mechanical computers are a subset, it's entirely possible to make a digital mechanical computer though it would be extremely slow).
  - 5y ago

derekp7 5y ago

There are some things that a slide rule is superior for -- one item I can think of is visualizing an arbitrary range of fractional values. For example, lets say you need a capacitor and a resistor with values in a particular ratio. Any pair will work in your given circuit (within reason), as long as that ratio is maintained. You have a drawer full of various resistors and another of capacitors, and need to find a pair that will work. So you set your slide rule to that fraction (let's say 1.7 / 3.3), and you can then pull up any resistor and determine which size capacitor can be used by glancing at the slide rule. (Of course you still have to keep track of the magnitudes in your head, but being in the habit of that makes you a better engineer anyway).

hilbert42 5y ago
"There are some things that a slide rule is superior for -- one item I can think of is visualizing an arbitrary range of fractional values." Exactly, similar to the way log scales make visualizing a range of results across the slide rule no matter what one is doing. Similarly, I have a number of good digital multimeters but I also keep several analog AVO meters, https://en.wikipedia.org/wiki/Avometer https://en.wikipedia.org/wiki/Avometer, to give me a sense of proportion if I'm adjusting something (nulling a discriminator etc.).
JKCalhoun 5y ago
I implemented Ohm's Law as you describe for an iOS App some years back [1]. Tried also to figure out how to do it in Javascript (still learning, love it if someone could really make it nice for the rest of us to use) [2]. [1] Perfboard (5th screenshot shows it): https://apps.apple.com/us/app/perfboard/id46595187 https://apps.apple.com/us/app/perfboard/id46595187 [2] SlideRule.js: https://github.com/EngineersNeedArt/SlideRule https://github.com/EngineersNeedArt/SlideRule

zabzonk 5y ago

When I was in school in the late 60s a slide-rule company gave a special offer to us, which all of our parents (wanting us to succeed in the bright technological future) duly bought into. As far as I know, none of us ever actually used them, preferring paper log tables. We were also taught how to use mechanical adding machines, possibly the last people to be lumbered with this information, which mercifully I have completely forgotten.

xyzzy21 5y ago
I was probably the last generation in the US in the 1970s to willingly learn slide rules - the HP-35 had been out a few years and new scientific calculators already made the demise of slide rules pretty obvious to even us nerdlets. One of my prized inheritances from my engineer father is his slide rule (complete with leather case).
- killjoywashere 5y ago
  I have a few slide rules at this point, including a Hemmi 200 "Made in Occupied Japan" https://www.sliderulemuseum.com/Hemmi.htm https://www.sliderulemuseum.com/Hemmi.htm
  - hilbert42 5y ago
    Thanks for the link. I've just seen my Sun Hemmi No. 130 System Darmstadt (which I'm looking at now and that I mentioned in my earlier post). It's still in excellent condition except the glass in the cursor has a crack in it).
- astangl 5y ago
  In our high school physics class in early 80s, the teacher didn't care for calculators, so you'd have to do your calculations by hand, or learn to use a slide rule. I learned to use a slide rule, along with a buddy. I don't remember others in the class using slide rules, but looking back now, I have a hard time believing everybody else used pencil & paper. So there were probably others. I think that teacher didn't retire for another 20 years, so he may have had kids in the 21st century still learning to use slide rules for his class.

xyzzy21 5y ago

Mathologer has a nice video about this via "log wheels". https://www.youtube.com/watch?v=ZIQQvxSXLhI https://www.youtube.com/watch?v=ZIQQvxSXLhI

albert_e 5y ago

For those who prefer this concept explained to you with a video and examples -- https://www.youtube.com/watch?v=waiprjueVpQ https://www.youtube.com/watch?v=waiprjueVpQ

jhallenworld 5y ago

A nice casual use case for a slide rule is metric conversion: https://americanhistory.si.edu/collections/search/object/nmah_1215014#:~:text=This%20ten%2Dinch%2C%20one%2D,of%20metric%20and%20conventional%20units https://americanhistory.si.edu/collections/search/object/nma.... Consider that this slide is doing two things for you: it remembers the conversion factor (for a bunch of difference conversions), and it does the multiplication or division.

ddingus 5y ago
I want one of these. Right now, I do this conversion a lot more than usual. Over time, I have mapped many of my familiar Imperial unit touchstone type references onto Standard International units, so I am largely good to go, but this would have been very useful during the process. And what I mean here is just ones sense of scale and ability to mentally estimate and work with familiar ratios to arrive at solid first order approximations. These are important, in that one can set expectations about the answer quickly and accurately. Doing that is a great check on the problem overall and or makes mental analysis quick and robust. It is all the little things, like a sheet of paper being 0.004" or 0.1mm. Looking at something, say to understand whether it can be manufactured, or maybe features are too small or large and fall outside process limits. Or, given a force, something happening, or one suspects may have happened, working backward to arrive at root cause of failure, having that kind of info "in head", useable directly in that internal way, knowing how it might appear, feel, be seen, sound like, is high value. Tools like this really help with all that. Combining the data with motions, the slide, how far, etc all build robust mental connections. It just starts happening. For me at least, I just begin to "know" whether it make sense, will fit, break, etc...
- spc476 5y ago
  I have four slide rulers, and all of them I picked up at various antique shops. The latest one I bought is the same type that the Apollo astronauts took to the moon (Picket N600-ES, about 6" (15.5cm) long). I paid about US$5 for it.
  - 5y ago

bediger4000 5y ago

I tried to find a place to buy a new slide rule for my 15-year old. I've got twins in different schools, one school doing a lot more math than the other, and I wanted to get him going on logarithms. Couldn't find a new one, just antiques on ebay, etc. I ended up making one of the paper ones, but they're not the same. Does anybody make new slide rules?

HappyJoy 5y ago
Maybe an E6B would be helpful.
floren 5y ago
I don't think anyone still makes new slide rules, except for the E6B flight computer which is rather specialized. However, you should be able to get a metal Pickett slide rule on ebay for a reasonable price; they're great slide rules and being metal rather than wood will tend to hold up better over the years (moisture can really mess up a wood slide rule). Something like this: https://www.ebay.com/itm/234503446574 https://www.ebay.com/itm/234503446574
- perilunar 5y ago
  > except for the E6B flight computer which is rather specialized That's a positive, not a negative, since it demonstrates a whole host of practical problems that can be solved quickly with a slide rule. And they still work fine for general multiplication, and they are cheap and easy to get.
derekp7 5y ago
You can buy refurbished and also new-in-box (a bit expensive depending on the model) slide rules from various sites, such as https://www.sphere.bc.ca/test/sruniverse.html https://www.sphere.bc.ca/test/sruniverse.html. I thought about getting into hand making them, figured out most of the techniques that I can do in my garage with some components (the end brackets, and cursor runners) being made on a 3D printer. But I'm hung up on where to get the cursor springs from, or what would be a good substitute. One of these days I may revisit the topic.
5y ago

jhallenworld 5y ago

For old calculating machines I want to recommend Prof. Chris Staecker's YouTube channel, his videos are enjoyable. Here is a play-list: https://www.youtube.com/watch?v=swCy6pQSEpk&list=PLLFpXNanTP9X6lHrX9qoJroqGAQRDDvV9 https://www.youtube.com/watch?v=swCy6pQSEpk&list=PLLFpXNanTP... Inspired me to buy a Comptometer: https://en.wikipedia.org/wiki/Comptometer https://en.wikipedia.org/wiki/Comptometer If all you need to do is add, Comptometers are the fastest machines so far invented. They are fast because you can enter entire numbers at once (as a "chord" with multiple fingers pressing multiple digits at once). No need to hit "+" key or pull a lever between numbers, each button press is an immediate addition. I'm thinking of making an electronic version- it would have the same Comptometer key layout, but have more operations (for example, hold multiply "shift" key down while entering number for a multiply).

pwr-electronics 5y ago
For graphical computation, I recommend Nomographer's YouTube channel https://www.youtube.com/channel/UCOLYtsL4ge6QfaAvBDeG1IA https://www.youtube.com/channel/UCOLYtsL4ge6QfaAvBDeG1IA

pkaye 5y ago

I think these are essentially nomograms. I seem to recall in college engineering back in 90s they taught us how to design nomograms for simple functions.

zanethomas 5y ago

That's what I had for a calculator in chemistry.

goache 5y ago

I recently created a web comic explaining slide rules! https://randomlyunique.com/plancky/2021/slide-rules/index.html https://randomlyunique.com/plancky/2021/slide-rules/index.ht...

ASalazarMX 5y ago
You comic is great, do you have an official RSS feed?
- goache 5y ago
  Oh wow - thanks for the compliment :-) https://randomlyunique.com/feeds/all.atom.xml https://randomlyunique.com/feeds/all.atom.xml

marcodiego 5y ago

I asked this once. The answer I got was: because "Log(x) + Log(y) = Log(XY), and the scales of a slide rule are logarithmic."

s0teri0s 5y ago

I love slide rules. I'm old enough to have had one with a belt case that I brought to school. But I have to ask, what is wrong with a ridiculous amount of precision?

GeorgeTirebiter 5y ago

https://www.sliderulemuseum.com/Manuals/M220_AnEasyIntroductionToTheSlideRule_IsaacAsimov_1965.pdf https://www.sliderulemuseum.com/Manuals/M220_AnEasyIntroduct... is the best book ever for a beginning slide rule user.

evilotto 5y ago

The ark lands after The Flood. Noah lets all the animals out. Says, "Go and multiply." Several months pass. Noah decides to check up on the animals. All are doing fine except a pair of snakes. "What's the problem?" says Noah. "Cut down some trees and let us live there", say the snakes. Noah follows their advice. Several more weeks pass. Noah checks on the snakes again. Lots of little snakes, everybody is happy. Noah asks, "Want to tell me how the trees helped?" "Certainly", say the snakes. "We're adders, and we need logs to multiply."

vincent-manis 5y ago
This reminds me of the cartoon diagram of a computer posted in our university's IBM 7044 computer room circa 1968. I've forgotten most of it, but I still remember the snake swimming in a little pool of water, subtitled “Floating-point adder”.

zwieback 5y ago

My sister is 3 years older and she still learned slide rule in high school but I didn't. Being a nerd I had my dad teach me though. One of the key things is just the right amount of grease in the tracks.

agumonkey 5y ago

I find this to be the most abstract yet primitive computing device. Bands and marks and you hop right into logarithmic relationships.

tedunangst 5y ago

> Notice that the 1 of the bottom is under π on the top bar. I spent a long time staring at the picture until I figured out the bottom is the second row, and there are four rows of numbers below the bottom.

throw0101a 5y ago

A comment from a previous discussion: --- The Professor Herning YT channel has a bunch of videos on both using slide rules and reviews/comparisons of various ones: * https://www.youtube.com/c/ProfessorHerning/videos https://www.youtube.com/c/ProfessorHerning/videos The "Practical Slide Rule" [0] and "Basic slide rule theory and use" [1] playlists are a good intro: [0] https://www.youtube.com/playlist?list=PL_qcL_RF-Zyu6ugp3E2nB9xoTSwpy1G-F https://www.youtube.com/playlist?list=PL_qcL_RF-Zyu6ugp3E2nB... [1] https://www.youtube.com/playlist?list=PL_qcL_RF-ZyvJYtIr9NRXJX958d6BgdbN https://www.youtube.com/playlist?list=PL_qcL_RF-ZyvJYtIr9NRX... --- https://news.ycombinator.com/item?id=30971066 https://news.ycombinator.com/item?id=30971066