Comments by "Kim O\x27Brien" (@kimobrien.) on "Mathologer" channel.

  1. I had both kinds at one time. You can also do square and cube roots by dividing the linear distance between one and your number in half or by a third. The advantage to the circular was the printing was on the wheel and it had two clear pointers you could set the distance between and unlike the stick kind you never had to worry about it falling apart on your way to and from class. Since accuracy is based on distance to print on the circular at four inches around was about as accurate as a 12 in rule. I think they also had trig functions on the wheel or with slide rules along with a linear scale and maybe one marked off from 0 to 90 or 360. Our high school math books came with trig and ln functions printed as tables in the books.
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  2. The sum of numbers 1+2+3+4...+100. Think of pairs of number that sum to 100, 99+1, 98+2, 97+3 ... 51+49 now you have 49 pairs which is 4900 plus 100 plus 50 which is the mid point adds up to 5050.
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