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I inherited two or three slide rules from my father. One of them is circular shaped. Once or twice he showed me how to do some basic calculations, and I've spen

I inherited two or three slide rules from my father. One of them is circular shaped. Once or twice he showed me how to do some basic calculations, and I've spent ten minutes here and there with various online tutorials, but I've never put the time in to actually understand it, so I always instantly forget how they work. Kind of a shame, but I hang on to them anyway. They're cool artifacts from the pre-computer world. Hm, I wonder if it could be a handy way to do fractional computation while I'm doing woodworking? If so, that could be a good excuse to finally learn how to use one. (Strangely, my work's proxy blocks this domain as "pornography." Interpret that as you will.)

toast0 3y ago
Most slide rules will do many operations, but the basic operation is multiplication. Multiplication on a slide rule works because you can turn multiplication into addition with X * Y = 10 ^ (log(X) + log(Y)) (Edit: i had e and ln up here, but 10 and log is a better match the slide rules from 1 to 10l The rules are log scaled, so you find X on one rule and line up 1 on the other rule, then look at what number on the first rule is where Y is on the second rule. Run a couple examples you know the answer to, and you'll get it. As I recall, wrapping/bounding is tricky, you might need to reverse X and Y or go the opposite way to get your answer. You'll need to do it like scientific notation as well, the rules only have numbers between 1 and 10. Division is inverted multiplication, so for X / Y, line up the rules so X and Y match, the quotient is what is on the X rule where Y is 1. I don't know much about woodworking, are you doing multiplication or division with fractions, or adding? Do you want fractional results or decimals?
- coldpie 3y ago
  Thanks! Usually adding and division. For example "7 3/4 plus 8 1/8" or "15 3/4 divided by 4." Fractional result would be ideal. I don't know if a sliderule is a good tool for this is or not :)
  - toast0 3y ago
    I think a slide rule isn't going to help much... You'll still need to do the addition, and then you'd need to eyeball 15 3/4 as a number between 1 and 2, do the division, and then eyeball the result into a fraction. I think I've only seen decimal marked slide rules, you could certainly have a fraction marked rule, but it wouldn't be that helpful, because 15 3/4 is not easy to turn into 10 * (1 + 1/2 + 3/4 * 1/5 ) And then you're not at a power of two fraction anymore either. Some other tool would be better; probably a pocket calculator that's taken advantage of half a century of computational advances and can manage fractions.
    - coldpie 3y ago
      Yeah, there's a ton of perfectly good fractional calculator apps and so on out there. I was just looking for an excuse to use my dad's old thing. Thanks again for the explanations.
  - bregma 3y ago
    No. A slide rule is all scientific notation (2 or 3 significant digits on the rule and you carry the mantissa in your head). Very good for accuracy but not so much for precision.
- Xerox9213 3y ago
  A lot of woodworking is done in inches and fractions of inches. Doing joinery where you have to consider things like the kerf of the blade often requires many annoying additions and subtractions of power-of-two denominators. While adding 3/16 and 5/32 is trivial, trying to do that while focusing on making a good cut and taking accurate measurements can be distracting.
duped 3y ago
> They're cool artifacts from the pre-computer world. I like slide rules, and abaci, and jigs, protractors, T squares, or other nifty tools for measuring and computing from "before" the computer age because they represent something of a unique tool. Every tool exists to perform some action better than can be done by some other tool or set of tools. And the interesting side of tools for solving math problems or measuring things directly or indirectly is that it's the foundation of abstraction. Breaking down a big problem into a smaller one that can be trivially done with another tool is foundational to how we develop technology. Like a pump moves water or a lever amplifies force, tools like a slide rule let us do less work but instead of manipulating physical forces they're reducing the amount of working memory and information we need to solve a problem. It's a level of ingenuity that's worth respecting.
crdrost 3y ago
Give you a woodworking example where it matters, see if it reaonates.. You’ve got a box 10" high, 15" wide, you want to decorate the side with a few raised panels with borders, whatever. You decide that they're going to be inset ¾" from the sides, middle one will be maybe 10% larger on each side, the double spacing of 1½" between seems too wide so you want to fudge to 1⅛". So all told width-wise you have a 15" span of which ¾ + 1⅛ + 1⅛ + ¾ is margin, so that’s 1½ + 2¼ = 3¾, you'll have 11¼ left over. You want to divide it into 1 + 1.1 + 1 = 3.1 pieces. So you locate axes A and B on your slide rule, these should be double log-log, going from 1 - 100, fine for multiplications. You will also see C and D, single log-log going from 1 to 10, higher in precision, also having them next to A and B allows you to perform square roots, use the hairline on the cursor to confirm that the square root of 16 is 4 for example. You also probably have a red series that is single log-log but backwards called CI, this can sometimes be helpful for divisions, and a maybe a K scale that is triple log-log allowing cubing or cube roots. Flip it over, you might have S for sine, t for tan, L for logarithm being a linear scale. Anyway, move the hairline on the cursor over A=11.25 to “remember” it, then put B=3.1 under the hairline and look at the place where B=1, it's around 3.625. Of course we would rather have this in eighths or 16ths, but look at (no sliding!) B=8 to find this is nearly A=29 or 29/8 inches, that 3.625 is 3⅝". And looking at B=1.1 you get that 10% larger is just 4". So you want a 4"×8½" panel in the middle, two 3⅝"×7¼" panels on the sides, you can again get that 7¼" by moving B=1.1 next to A=8.5 and then B=1 shows 7 and change, peek up at B = 4,8,16 to see if it's best written as a quarter or eighth or sixteenth fraction. So they're great at - multiplying or dividing numbers, especially if they are not round - converting those decimals to eighths or sixteenths, calculators just give you digits usually, slide rules you can quickly see what is 1x this number, 2x, 4x, 8x, 16x, makes it a snap.
- twic 3y ago
  Sounds like i might even be able to crack CSS layouts with one of these things.

toast0 3y ago

Most slide rules will do many operations, but the basic operation is multiplication. Multiplication on a slide rule works because you can turn multiplication into addition with X * Y = 10 ^ (log(X) + log(Y)) (Edit: i had e and ln up here, but 10 and log is a better match the slide rules from 1 to 10l The rules are log scaled, so you find X on one rule and line up 1 on the other rule, then look at what number on the first rule is where Y is on the second rule. Run a couple examples you know the answer to, and you'll get it. As I recall, wrapping/bounding is tricky, you might need to reverse X and Y or go the opposite way to get your answer. You'll need to do it like scientific notation as well, the rules only have numbers between 1 and 10. Division is inverted multiplication, so for X / Y, line up the rules so X and Y match, the quotient is what is on the X rule where Y is 1. I don't know much about woodworking, are you doing multiplication or division with fractions, or adding? Do you want fractional results or decimals?

coldpie 3y ago
Thanks! Usually adding and division. For example "7 3/4 plus 8 1/8" or "15 3/4 divided by 4." Fractional result would be ideal. I don't know if a sliderule is a good tool for this is or not :)
- toast0 3y ago
  I think a slide rule isn't going to help much... You'll still need to do the addition, and then you'd need to eyeball 15 3/4 as a number between 1 and 2, do the division, and then eyeball the result into a fraction. I think I've only seen decimal marked slide rules, you could certainly have a fraction marked rule, but it wouldn't be that helpful, because 15 3/4 is not easy to turn into 10 * (1 + 1/2 + 3/4 * 1/5 ) And then you're not at a power of two fraction anymore either. Some other tool would be better; probably a pocket calculator that's taken advantage of half a century of computational advances and can manage fractions.
  - coldpie 3y ago
    Yeah, there's a ton of perfectly good fractional calculator apps and so on out there. I was just looking for an excuse to use my dad's old thing. Thanks again for the explanations.
- bregma 3y ago
  No. A slide rule is all scientific notation (2 or 3 significant digits on the rule and you carry the mantissa in your head). Very good for accuracy but not so much for precision.
Xerox9213 3y ago
A lot of woodworking is done in inches and fractions of inches. Doing joinery where you have to consider things like the kerf of the blade often requires many annoying additions and subtractions of power-of-two denominators. While adding 3/16 and 5/32 is trivial, trying to do that while focusing on making a good cut and taking accurate measurements can be distracting.

duped 3y ago

> They're cool artifacts from the pre-computer world. I like slide rules, and abaci, and jigs, protractors, T squares, or other nifty tools for measuring and computing from "before" the computer age because they represent something of a unique tool. Every tool exists to perform some action better than can be done by some other tool or set of tools. And the interesting side of tools for solving math problems or measuring things directly or indirectly is that it's the foundation of abstraction. Breaking down a big problem into a smaller one that can be trivially done with another tool is foundational to how we develop technology. Like a pump moves water or a lever amplifies force, tools like a slide rule let us do less work but instead of manipulating physical forces they're reducing the amount of working memory and information we need to solve a problem. It's a level of ingenuity that's worth respecting.

crdrost 3y ago

Give you a woodworking example where it matters, see if it reaonates.. You’ve got a box 10" high, 15" wide, you want to decorate the side with a few raised panels with borders, whatever. You decide that they're going to be inset ¾" from the sides, middle one will be maybe 10% larger on each side, the double spacing of 1½" between seems too wide so you want to fudge to 1⅛". So all told width-wise you have a 15" span of which ¾ + 1⅛ + 1⅛ + ¾ is margin, so that’s 1½ + 2¼ = 3¾, you'll have 11¼ left over. You want to divide it into 1 + 1.1 + 1 = 3.1 pieces. So you locate axes A and B on your slide rule, these should be double log-log, going from 1 - 100, fine for multiplications. You will also see C and D, single log-log going from 1 to 10, higher in precision, also having them next to A and B allows you to perform square roots, use the hairline on the cursor to confirm that the square root of 16 is 4 for example. You also probably have a red series that is single log-log but backwards called CI, this can sometimes be helpful for divisions, and a maybe a K scale that is triple log-log allowing cubing or cube roots. Flip it over, you might have S for sine, t for tan, L for logarithm being a linear scale. Anyway, move the hairline on the cursor over A=11.25 to “remember” it, then put B=3.1 under the hairline and look at the place where B=1, it's around 3.625. Of course we would rather have this in eighths or 16ths, but look at (no sliding!) B=8 to find this is nearly A=29 or 29/8 inches, that 3.625 is 3⅝". And looking at B=1.1 you get that 10% larger is just 4". So you want a 4"×8½" panel in the middle, two 3⅝"×7¼" panels on the sides, you can again get that 7¼" by moving B=1.1 next to A=8.5 and then B=1 shows 7 and change, peek up at B = 4,8,16 to see if it's best written as a quarter or eighth or sixteenth fraction. So they're great at - multiplying or dividing numbers, especially if they are not round - converting those decimals to eighths or sixteenths, calculators just give you digits usually, slide rules you can quickly see what is 1x this number, 2x, 4x, 8x, 16x, makes it a snap.

twic 3y ago
Sounds like i might even be able to crack CSS layouts with one of these things.