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Ask HN: Is there anyone here who still uses slide rules?

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Re: Ask HN: Is there anyone here who still uses slide rules?

#81
post #6

I have two or three that I inherited from my dad. I've never learned to use them because I haven't thought of something I'd use them for. The one thing I could think of is quickly doing fractional math while woodworking (what width will I have if I rip this 7.5" board into 4 pieces?) but in reality I just don't actually do that much math while woodworking.

As mentioned elsewhere you can use them in the kitchen if you start wanting to scale recipes at will - it's easy to double, but with a slide rule you can quickly get other ratios.

Works better when you do things by weight and metrically, no doubt.

Re: Ask HN: Is there anyone here who still uses slide rules?

#82

Earlier quoted context omitted.

A key idea is that addition for logs is equivalent to multiplication. To multiply two numbers you line them up on a log scale and then read out the sum, which is equivalent to the product. There is much more they can do but that was one aha moment when my dad showed me his.

I've never used a slide rule but recently developed an interest in them (and also in nomograms [1]) My fascination stems from a belief: that slide rule usage helps users develop a certain intuition for numbers whereas the calculator doesn't. To illustrate, suppose someone tries to multiply 123 and 987 with a calculator but incorrectly punches in 123 and 187. My hypothesis is they'll look at the result but won't suspe…

> nomograms

Me too!

Nomograms are cool. They're little charts that let you compute a function physically, e.g. by lining up a ruler. A nomogram isn't a picture of a function: it is the function. If you're clever, you can make a nomogram that encodes complicated nonlinear mappings or even complex-valued relationships on a 2D plane.

Occasionally nomograms are just better too: because they're continuous and analog, they can naturally express things digital logic people can do only awkwardly, just like Rust people can only awkward approximate things natural in Verilog (e.g. truly parallel CAM search).

Nomograms are basically the tabletop gaming of math. Like a good tabletop game, a good nomogram requires a special kind of cleverness. Sure, coding something like Factorio is also hard: but it runs on a CPU. Something as rich and complex as Power Grid and High Frontier? Running on cardboard? Whole other level.

I recall one tabletop two-player game that featured a single-player mode in which you played against an "AI" that you ran by hand by moving cardboard pieces around on a game-provided template under pseudocode-ish rules from the game manual. It's hard enough to code a decent game AI with all the resources of a CPU at your disposal. It's an OOM harder to do it when you're limited to physically-realized lookup tables, a literal handful of registers, and a scant few clock cycles of logic per turn.

Coming full circle, some of these tabletop game "AI"s incorporate nomograms to help them fit their logic within the constraints.

Example of a cool nomogram: https://en.wikipedia.org/wiki/Smith_chart. Smith charts let you compute complex (pun intended) relationships in RF signal processing with just a compass and straightedge.

Also: part of the fun in making nomograms is that there's no general procedure you can follow to make a good one, just like there's no general compiler from computer game to tabletop game. They're art: specifically, one of those forms of art that, like architecture, has to meet functional requirements while tickling our aesthetic sense. It's kind of funny how when you optimize this kind of art for aesthetics under their functional constraints, you end up supercharging the functional part by side effect somehow.

Re: Ask HN: Is there anyone here who still uses slide rules?

#83
Following a post on HN a few weeks ago, I bought a used one to use in the kitchen for scaling recipes. It has to be a linear one for that, not circular, so you can set it and read it without touching it again. I also have one in my "apocalypse kit" in case of, I dunno, an EMP?

My dad was an engineer in the slide rule era and taught me how to use one when I was a kid. He said when he was in college all the engineering students had them hanging from their belts in leather sheaths like gladiator swords and they would slap when they walked.

Re: Ask HN: Is there anyone here who still uses slide rules?

#84
post #51

I designed and 3D-printed my own slide rule to help me play Balatro! Balatro is a roguelike survival game where you need to multiply "chips" and "mult" together to meet a requirement each round. You get three chances to draft enough resources to survive. I designed my own slide rule to help with the mental multiplication - most of the fun of the game comes from the mechanics being slightly obscured from the player. S…

You almost have to do this, or buy a used one at a markup, as nobody seems to make them anymore (except circular ones).

Re: Ask HN: Is there anyone here who still uses slide rules?

#87
post #17

When I was in high school, (early 1990s,) there was a giant one mounted above the blackboard. It was clearly used for instruction in the past, but it looked so cool that no one wanted to remove it. Every once in awhile a teacher would spend about 10-15 minutes showing how to use it. Everyone would "oooh" and "awww" and then we would all laugh about how we didn't need to use them now that we all had calculators in our…

> we all had calculators in our pocket that were more powerful than the computers that put people on the moon. Pencils and slide rules are what got us to the moon, and back to Earth. Pencils and slide rules.

And “computers,” the people kind.

Re: Ask HN: Is there anyone here who still uses slide rules?

#88

A big 6-foot K&E sliderule hung at the front of my high-school chemistry classroom, but was never used. At graduation ('91) I asked the teacher if I could have the slide rule and she said "sure". I keep it now in my office, and once a year I bring to the data visualization class I teach at UChicago, to show how it works, and to show it as an example of a visual device in aid of computational thinking (nomographs bein…

There is also the Vernier scale on certain styles of mechanical calipers.

I love the Vernier scales! But I honestly hadn't known about the sense in which slide rules have a Venier scale until your comment, which led me to [1]. In another class on laser-cutting I had students make a kerf-meter, which became more accurate with a Vernier scale.

[1] https://dram.page/p/slide-rule-vernier/

Re: Ask HN: Is there anyone here who still uses slide rules?

#89

I have one on my watch. It’s a citizen with a circular slide rule /E6B flight computer. I need my reading glasses to use it, but it’s fun. It can reliably get me 2 sig figs, and a decent guess at a third. But… if I think about it for a minute, I can usually get that in my head anyway. Being able to setup a ratio is great though for unit conversions and things. It’s also really good for answering that question when dr…

I have a Rotary Henley Chronograph and love using it for baking ratios.

Re: Ask HN: Is there anyone here who still uses slide rules?

#90
post #51

I designed and 3D-printed my own slide rule to help me play Balatro! Balatro is a roguelike survival game where you need to multiply "chips" and "mult" together to meet a requirement each round. You get three chances to draft enough resources to survive. I designed my own slide rule to help with the mental multiplication - most of the fun of the game comes from the mechanics being slightly obscured from the player. S…

How much did it help? How far have you ascended?

right, i'm still absolute rubbish at the game but it's been a great learning experience!
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