Before we needed batteries we had slide rules, which even came in pocket sizes. The theory was that to multiply two numbers you'd add the log of both numbers (now you know why we had log tables). This is also why the scale lengths on a slide rule are log scales and not evenly distanced number scales. It is brilliantly simple once you see how to use it. In case you wondered how you'd work with large numbers such as 235 x 648, everything gets reduced to under 10 so 235 would be 2.35 and once you finish calculating you change the magnitude )decimal point position) back, so some common sense is needed.
I remember having to learn to use log tables at school in the late 1970's but I did not really understand why as pocket calculators had appeared although we were not allowed to use them in school at that time. I was caught in an era where log tables were still being taught but slide rules had already been largely replaced by calculators and the use of log tables was a bit lost on us.
but you can also watch a video which may show the use a bit more clearly at https://youtu.be/uAGCDTtIahY
#mathematics How to Use a Slide Rule
I’ve always felt a little left out of the traditional nerd stereotypes. I don’t wear glasses, my lady clothes have no real pockets so I can’t use a pocket protector, and I was born well after the reign of the slide rule. But in the spirit of Analog Week, I’m trying to learn.