But I'm going further back in time to see if there is anybody here who still uses slide rules?
But I'm going further back in time to see if there is anybody here who still uses slide rules?
Works better when you do things by weight and metrically, no doubt.
I also have one of these: https://archive.org/details/spencersdecimalr0000unse ; I believe they were popular around the time of the UK converting to decimal currency, to save people having to do the transitional arithmetic. Had a bunch of other tables in. A physical LUT.
I wonder if there's anyone with abacus skills here. I hear that held out against calculators a lot longer, for shopkeeper uses.
I have his slide rule, that he used for ages. It's a mystery in a box to me - I have not the foggiest clue how it is used - but I cherish it.
It's easier and more straightforward than you might expect. I encourage you to learn to use his slide rule, in large part because you might find it fun, but also to honor your grandfather's legacy.
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 suspect any problem. The equivalent operation on a slide rule requires fewer physical actions and hence, is less error prone.
Do you think there's anything to this hypothesis?
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.
With a slide rule you can only multiply the significant digits, not the magnitudes -- which you have to do in your head. So you do exactly the same thing with the slide rule to multiply 123 and 987, 1.23 and 9.87, and 1,230 and 9,870. In all three cases, you get exactly the same answer: 121 or maybe just 120 (you only get 3 digits of precision at best). You still have to multiply the powers of ten in your head, to get the answers 121,000, 12.1, and 12,100,000.
I am just old enough to belong to the last generation of slide rule users. I used them in high school and college, then scientific calculators came along.
One you understand slide rules and logarithms, it is easier to understand convolutions in the FFT (frequency) domain...
Almost like programming in APL, where you can solve a problem by expanding it in extra dimensions and getting the answer by re-compacting the complex object using a different view.
He gave me his slide rule probably a year or so before he passed away. I've got it sitting on my desk and always makes me think of him. Like you, I've got no idea how to use it (even though he tried to explain it to me), so maybe the other comments here can fill in the gaps for me :)
slide rules are happiest when they're used and worn out. they need exercise and sunlight
https://social.bau-ha.us/@raganwald/115979168665997624
Although slide rules are a "dead skill," Aviators typically learn to use something called an E6B Flight Computer, which works on the same principle as a round slide rule.
https://pilotinstitute.com/e6b-made-easy/
I have one in my flight bag and was required to demonstrate proficiency in its use. Of course we fly with connected digital devices these days, but having an analogue backup that operates even if the power fails is important.
A beautiful device... though I have to admit after getting the certificate I exclusively use Foreflight.
Some of it is pure nostalgia, though, I’ll admit. It a way to honor how people solved similar problems in the past. In the 18th century a sextant plus accurate chronometer or lunar distance table was one of the pivotal technologies of the age; you could use it to pinpoint your location on the boundless ocean within a few miles. That demands respect, and it’s also just really cool it was possible in an era before electricity and radio.
Heh heh, I was in the Sailing Cub in high school, and our Sailing Master (RIP Master Gibb) said literally the same thing about learning to navigate with sextant and chronometer even though we never sailed out of sight of land. It was all about deep respect for the history and tradition of being a Mariner.
Now I fly gliders, "the purest form of flight," and while you can get a glider with electrically operated landing gear, a jet sustainer engine, and digital navigation and flight computing devices...
There is something extraordinarily pure about the exercise of flying with everything electrical turned off (except for the transponder and radio for safety). And even purer... Flying with covered instruments so we don't even get analogue airspeed and altitude.
Circling back to slide rules... Sometimes we crave that simplicity, that direct experience of a thing.
This guy gets it.
[You Need A Kitchen Slide Rule](https://entropicthoughts.com/kitchen-slide-rule)
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 pocket that were more powerful than the computers that put people on the moon.
It's always nice to learn about the past so we can appreciate what we have now.
Pencils and slide rules are what got us to the moon, and back to Earth. Pencils and slide rules.
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 being another great example).
I think I can do basic calculations with them, although I really haven't touched one in many years.
I will note I didn't get it or use it until about 1998.
I'm not old enough to have used them to do calculations, but I find them extremely useful to explain logarithms and how multiplication can be represented by the sum of logarithms. I actually work with grad students who should know these things, but watching it in a slide rule on their hands really helps to build intuition.
I used it a few times, it works, of course, ... but it's not fast and not precise so I don't think anybody would use it to be productive in 2026
It sits in a box
I have no use for them on a day-to-day basis, though. An abacus is more useful for things like counting board game points and adding up taxes.
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 driving where you’re like, ok if I go 10mph faster how much sooner will I get there which is otherwise hard to do mentally.
Most of the benefit of using a slide rule in my experience comes not from using it, but from thinking LIKE you’re going to use a slide rule. You learn to freely use scientific notation with ease, and mental estimation to get the order of magnitude right.
And just my 2 cents, but circular slide rules are where it’s at.
This is what I was trying to get at in my other comment [1]!
They're really cool
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.
Since I designed this slide rule myself, I was able to make a couple unconventional design choices that fit my needs. For instance, mine has three octaves so it can represent numbers within the ones, thousands, or millions' range, for example; no need to track arbitrary powers of ten. Since it's a rotary rule, it wraps around. Eg. 353×24 shows on the device as 8.47, so you can think of it as 8.47 thousand, for example.
Holding a physical object in my hands while playing helps more than I thought it would. Should I take a card that increases chips by 600 or increases mult by 1.3×? Do I need to take a card to clear the blind in the short term, or do I have enough resources to draft a slower card that will scale better over time? Even just looking at how densely packed the marks are on the "Chips" side vs the "Mult" side of the device gives a visceral physical sense of what my build needs to focus on.
Pictures and .STL: https://www.printables.com/model/1026662-jimbos-rotary-slide...
Github repository: https://github.com/gcr/balatro-slide-rule
The actual plotting code used Marimo notebooks, which host a python in your browser via WASM. Take a look here: https://marimo.app/l/4i15d7
I entered it in Printables’ educational tools competition but the other entries were cooler. Maybe HN might like it. :-)
[1] https://www.sliderulemuseum.com/REF/scales/MakeYourOwnSlideR...
[2] http://leewm.freeshell.org/origami/card-slide.pdf
[3] https://www.sliderulemuseum.com/SR_Scales.shtml#YingHum
[4] http://www.antiquark.com/sliderule/sim/virtual-slide-rule.ht...
It also scares the crap out of me to think about what infinity is: you see your slide manipulate incredible numbers, then you imagine a slide that is twice as big. Or a few feet long.
"The Analytical Rule might be considered a distant relation – as a skyscraper is to a shack – of that kindergarten toy, the logarithmic Slide Rule. Darell used it with the wristflip of long practice. He made freehand drawings of the result and, as Anthor stated, there were featureless plateaus in frontal lobe regions where strong swings should have been expected."
I'd really love an Analytical Rule, this hoverboard of the early atomic era.
I have one on my desk that I often use for quick estimations. It boots up in zero seconds.
Countertops is an industry with all the modern tools but 5000yo approach.
One of our teachers allowed us to bring a single page of notes to the exam. I wrote my notes on a photocopy of a slide rule. At exam time, I tore the sheet in half.
Of course the teacher thought I was being a smart-ass, and given that the tests were written when calculators were not allowed, they were never really all that useful.
In college chemistry, at each exam, they handed out a sheet that had the periodic table on one side, and a table of logarithms on the other.
Typically to do a calc I fire up Excel or the calc on my phone, bang in the numbers and accept the result without thinking. It's that "without thinking" part that is dangerous. The slide rule is slow and physical and forces my brain to think about the inputs. Another nice feature is that it can give you quick answers when you aren't sure of the accuracy of the inputs. eg if 2 * 4 was really 1.8*4.1, what would the answer be? It's quicker to see that on a slide rule (one tap on the ruler) than punch in 7 characters.
Fastest and best feedback for whether the batting team is ahead of the rate.
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.
My mom found my shellback card among some stuff in her basement and asked if I’d like her to send it to me. Yes, please! Darned if I want to earn a replacement card.
kayo_20211030•3h ago