- To add to this, there's a great set of resources by Joe Pasquale explaining the mathematical theory behind how various functions can be computed by slide rules:
* https://cseweb.ucsd.edu/~pasquale/Classes/SlideRule/
* Mathematical Foundations of the Slide Rule (PDF): https://cseweb.ucsd.edu/~pasquale/Papers/IM11.pdf
* Why Does A Slide Rule Work? (PDF): https://cseweb.ucsd.edu/~pasquale/SlideRuleTalkLasVegas14.pd...
The gist of it is:
1. First, define a way to represent any univariate monotonic function f(x) on a graduated scale. (Specifically: select a discrete set of x values, and for each of these x values, place a mark with label x at a distance proportional to (f(x) - f(x_L)) from the left endpoint, where x_L is the leftmost x value.)
2. Then, if we have two such scales f(x) and g(x) that can slide relative to each other, we can compute functions of the form h(x, y, z) = f_inverse(f(x) + g(y) - g(z)).
It ends up being surprisingly versatile -- the above resources show how you can compute:
1. Multiplication: x * y using f(x) = log(x) and g(y) = log(y), with z fixed at 1
2. Hypotenuse: sqrt(x^2 + y^2) using f(x) = x^2 and g(y) = y^2, with z fixed at 0
3. Parallel resistors: 1/(1/x + 1/y) using f(x) = 1/x and g(y) = 1/y, with z fixed at +infinity
4. Exponentiation: x^(y/z) using f(x) = log(log(x)) and g(y) = log(y)
- In the UK there was a time (late `70s) when slide-rules were allowed in examinations but calculators weren't, no-brainer to learn how to use one just for that. Even better, if you added "(SR)" after your calculations, that indicated that you had used a slide-rule so small errors were permitted.
by throw0101a
1 subcomments
- This education film from 1957 gives a good overview of using one:
* https://www.youtube.com/watch?v=oYQdKbQ-sgM
"Professor Herning" (?) also has a good series of videos on the use of various scales as well:
* https://www.youtube.com/@ProfessorHerning/videos
His playlist starting at the beginning (C and D scales) with a Manheim layout:
* https://www.youtube.com/playlist?list=PL_qcL_RF-ZyvWJJkJOk_O...
* https://sliderulemuseum.com/Manuals/M37_Post_Manheim_Instruc...
Some manuals / books on slide rules:
* 1909: https://archive.org/details/mannheimsliderul00coxwrich
* 1922: https://archive.org/details/cu31924002978561/mode/2up
by smusamashah
0 subcomment
- Here one can play with many slide rules in the browser https://www.sliderulemuseum.com/VirtualSR.shtml
by JKCalhoun
1 subcomments
- Deep dive, for sure. I suspect Cliff Stoll is enjoying this site.
I played with creating a logarithmic slider thing [1] in Javascript that I hoped I could package up as a kind of "widget" people could use on their web pages. But I don't really know Javascript that well—or rather how to make an API out of a Javascript thing.
Anyway, to test it I tried to make an Ohm's Law calculator [2].
I would love to see a site like the one in this post have some kind of interactive slide rule on the web page itself.
[1] https://github.com/EngineersNeedArt/SlideRule
[2] https://www.engineersneedart.com/ohmslaw/index.html (the yellow slider is not directly user-moveable in this example)
- My Dad is a retired R&D chemist who worked at the DuPont corporation's Experimental Station. When I was a kid he would bring his old slide rules home from work when he got a new one, and at one point he explained to me how they work but I forgot it all long ago.
I still have the slide rules, so this post was a great rabbit hole to go down. In software there's no need for them but I still find them fascinating as a window into how engineers used to get their work done.
- Last year I made my own rotary slide rule for playing Balatro, the poker roguelike!
My version has a couple interesting properties compared to ordinary linear slide rules:
1. It has three octaves, so it can scale from 1 to 1k or from 1k to 1m, or from 1m to 1b. This is great for calculating point values
2. It's rotary
3. It can be easily 3d-printed!
Source code and .STL files here: https://www.printables.com/model/1026662-jimbos-rotary-slide...
- These fascinates me, it's one of the highest simplicity / abstraction level ratio I can think of. A few marks well spaced on two bits of wood, and you get "linearized" multiplication. Nicest ~analog computer I can think of :)
- For people into watches, check out this video (and the whole series of watch and learn) on slide rules on watches: https://www.youtube.com/watch?v=RuK_77DEUfw
by clickety_clack
2 subcomments
- Slide rules are super cool. Such an easy gift to give the engineer in your life.
I never spent the time to get quick with it, but I could absolutely see it being quicker than a calculator. You’d just have to be aware of the limits to its precision if you were in a field that required it.
- In my head: “Oh yeah, I forgot how to use one of those”
This article: “lol, is that the depth of your commitment”
by vjvjvjvjghv
1 subcomments
- When I was in 5th grade, calculators had become pretty affordable and there was this huge discussion whether kids should learn slide rules or use calculators. At the time it was decided we should learn slide rules and I am happy about this because it gives you some level of number intuition.
It reminds me a little of AI now. The question of whether students should use AI will probably soon go away and everybody will use AI. Not sure what the results will be.
- I have one at home, which is the one we had to buy to use in highschool. In the math classrooms we had a 6 feet version that could be mounted on the blackboard such that the teacher could used for instruction. See for a picture on the Dutch page https://rekenlat.barneveld.com/rekenliniaal.htm
by entaloneralie
0 subcomment
- I have a little collection of them.
I keep the small Hemmi bamboo on the navigation table at all time.
https://wiki.xxiivv.com/site/slide_rule
by zeckalpha
4 subcomments
- Anyone know of a good place to buy a new linear slide rule? I know there's a circular slide rule manufacturer but am not sure if any linears are being made any longer.
by jamesgill
1 subcomments
- Last week I donated several slide rules to Goodwill; a few were very nice. Meanwhile, I still have a pristine HP-41cx and HP-15c, and an HP-25 app on my iPhone.
- While I'm a bit too young to have used one in school, my dad did give me his slide rule from when he was a student. It's one of my most prized possessions, if only to show how far humanity has come in terms of computing devices.
- A sort of non-logarithmic slide rule, the E6B Flight Computer, was still in use when I was a student pilot 20 years ago. I still carry one: they don't require electricity (although using one in the dark requires a light source).
https://en.wikipedia.org/wiki/E6B
- It is worth keeping one around.
When the "cloud" is raining and your laptop and phone batteries are drained and you suddenly need to navigate your 4823 times table - its got you covered.
You will also need to work out how to write with a pen or pencil on paper or try and fix up your atrophied ability to remember arbitrary "facts" short term.
- I still have the wooden 10" Keuffel and Esser that I inherited from my father and that I used in college. These days I use my HP15C unless I want to provoke glee and amusement in my younger colleagues by sporting my Pickett slide rule in my shirt pocket.
by inamberclad
0 subcomment
- For the past 10 years, I've worn a slide rule every day. It's a small circular one modeled after the E6B aviation slide rule, with markers for common aviation conversions.
by NetMageSCW
0 subcomment
- The HP-35 wasn’t programmable- it was just a scientific calculator.
by kingforaday
0 subcomment
- This would have been helpful for Sam Cooke.
- I came up on the cusp of the calculator take-over, so although slide rules were around, and we were taught how to use them in school, I never really used them for any practical purpose. However, since they were the buggy whips of that day, you could pick up nice fancy ones for cheap in stationary stores (also now gone). So somewhere I have a good collection of them.
by John-Tony12
0 subcomment
- [dead]
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