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Comment by KineticLensman | Hacker News Reader

Alas! No specific mention of the circular slide rule [0]. I have one in my desk drawer that I inherited from my dad - who used it in the 1970s to confirm his hip hacker credentials to his colleagues (they were building the control circuits for early radio-therapy machines in a cancer research institute).

[0] https://americanhistory.si.edu/collections/object-groups/sli...

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Circular slide rules tend to have smaller scales which may be harder to read but being circular has a great advantage. Look at how much effort in the OP is devoted to cases where the answer would ordinarily be off the end of the scale.

I was curious about circular slide rules, and found one on eBay for a few bucks, so what the heck. It turned out that it was a give-away from a company that used to be in my town, so I ended up having a nice conversation with the seller about his history with the company and so forth. He was a long retired engineer.

Anyway, I started playing with ratios, and noticed that the thing is inaccurate! Further inspection and hypothesizing led me to discover that the scales were not printed concentrically with the mechanism. It's very slight, and not critical to my work in any way, so I treat it as part of the learning experience.

Still very much in use: the E6B! https://en.wikipedia.org/wiki/E6B

My dad was a USAF fighter pilot; he kept his in-flight circular slide rule around for years. Unfortunately I didn't see it around when clearing out the house out after he and my mother died; I know I'd have kept it (because I've still got my yellow Pickett aluminum Model N-500-ES, © 1962).

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