Mar. 14th, 2014

rbandrews: (Default)
I sort of went nuts on eBay the other day and ordered a few slide rules. Today the first ones came in: a K&E "beginner's slide rule" with only four scales (A, B, C, and D), and another little pocket one with some trig scales, but no folded scales and broken indicator. I realized these were in pretty bad shape when I bought them, but it was $5 for the pair, so I bid to see what would happen.

So, slide rules are essentially a collection of weird-scale rulers that you can line up against each other in different ways. The scales are all labeled with standard names that say what they are. The basic scales that all rulers have are C and D, which are log scales, used for multiplication: since log(x) + log(y) = log(xy), if you line up the start of the C scale with some number on D, then see what's across from another number on C, you multiply those two numbers.

A and B are also log scales, but compressed so that they show ten times the range. CI is a log scale just like C but backwards, used for making division easier.

Anyway, I now have four slide rules. Only one of them, the first one I got, has a bunch of fancy scales, though, and I want to get another one like it. I've got a couple more auctions I've won for odd slide rules, that I'll probably post about when I get them.

I did finish the Asimov slide rule book last night. It was great, especially for someone into recreational math. I was a little disappointed that he didn't go into the more fancy log-log scales on my K&E rule (used for raising things to arbitrary powers), but it's kind of expected since almost no slide rules seem to have had them and almost no one would ever need to use one anyway.

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