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. :-)

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.

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).

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.

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.

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.

[You Need A Kitchen Slide Rule](https://entropicthoughts.com/kitchen-slide-rule)

I have one on my desk that I often use for quick estimations. It boots up in zero seconds.

https://en.wikipedia.org/wiki/E6B

https://en.wikipedia.org/wiki/Keuffel_and_Esser

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.

https://www.arithmeum.uni-bonn.de/en/arithmeum.html

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.

The authors commented "If you get really interested you can make much more accurate slide rules, or you can buy them for about £1." I fear not any more...

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.

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.

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.

Fastest and best feedback for whether the batting team is ahead of the rate.

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.

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.

https://www.flickr.com/photos/jonsphotos/218609214/

https://news.ycombinator.com/item?id=45985196

My favorites from my collection are a little Dietzgen No 1773, which is surprisingly featureful for something that can fit in a pocket, and a Faber-Castell Novo-Biplex 2/83N, which is kind of one of the big guns for slide rules.

Countertops is an industry with all the modern tools but 5000yo approach.

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

"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.