Old-school calculation

For my birthday my mom gave me, among other things, her old slide rule.This is more than a lowly one, but a fairly schmick one from K&E. Keuffel & Esser is a high-end manufacturer of these slide rules. This is the model 4083-3 that from what I can tell was made between 1955 and 1962.From the scales and looking at a fan site (!) it seems to match everything that should be there.This got me thinking. I grew up around this guy. I grew up playing with it knowing that it could be used for something useful, but all I ever did with it was slide it back and forth and probably generally annoy my mother by playing with a precision instrument.Sitting on the kitchen counter here in Seattle I wanted to figure out how to use it -- at least in a primitive way.This got me rabbit-holed into slide rules in general.I even found a 183-page manual for the use of a high-end slide rule. (Yes, I have a bid on one on ebay -- sue me)So here's a simple calculation: 42 x 7.What I did was set the slide (the 1 next to the K+E logo) to 4.2. I can set either side (this is one decade of a log scale) to 4.2 but I have to pick with one will get me a result without going off-scale. The proper name is I'm setting the C scale to 4.2.This actually gets into a quirk of slide rules. No decimal points. It's up to you to figure out where it should go.Next, I set the hairline to 7 since I'm multiplying by 7. Actually, like before this could be multiplying by 7, or 70 or .7 or anything like that -- I'd set it to 7Now I read the D scale. It reads 2.94. The bigger lines on that scale are .10's. The hair-line is sitting 3 ticks from 3 and each small tick is .02, hence 2.94.Now we have to deal with decimal points. In the case of 7 x 42 it'll be more than 100 and less than a 1000 so the answer is 294.If you do the math on your computer, you'll invariably come to the same result. :-)Now, all I have to do is figure out all the log-log scales and such. More brain work.

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Now, if the zombies come I'll have the ability to both defend myself and my family and the ability to do math without a source of power! :-P