Scales for building your own slide rule (1999) | Hacker News Reader

Scales for building your own slide rule (1999)

sliderulemuseum.com

23 pointsTomte5 comments

It's not hard to get a reasonable approximation of a slide rule working with a few pieces of material that can slide past each other, and a bit of iteration. When I was young, I thought it would be cool to build a really long, high precision slide rule out of metal, not so much any more. ;-)

Just starting with the fact that 2^10 is almost exactly 10^3 gets you started pretty quickly, You can mark out the powers of 2 spaced linearly, 1 to 1024, then divide by 3 to get a fairly good approximation of 10. You should be able to fairly quickly get marks for the rest of the numbers to 10.

Try it with a pencil, compass, and some pieces of paper... it's a fun exercise.

This way you can get the 9 evenly spaced aproximate numbers

  1.28 = 128/100
  1.6 = 16/10
  2
  2.56 = 256/100
  3.2 = 32/10
  4
  5.12 = 512/100
  6.4 = 64/10
  8

Do you have any more tricks?

Edit: Searching my memory I now remember the fact

  2^16/3^8 ~= 10

which can be used iteratively to pen-and-paper generate another 7 evenly spaced numbers

  2*2/3 (1. number) *2*2/3 (2. number) *2*2/3 ...

I've always wanted to make one of those giant 10-foot slide rules that hung in our science classrooms when I was in high school.

Now that I own considerable acreage, with this I no longer have to limit myself to 10 feet. Heck, I can probably go for 4 or 5 significant digits if I can find the right lumber.

"The World's Longest Slide Rule, The Texas Magnum is 350 feet 6.6 inches and holds the world's record."

You just started my idea generator: Why not hundreds of feet of tape moving between two wheels like and old tape recorder. Two tapes on two pairs of wheels. Roll one tape till the first number is visible; roll the second tape till the second number aligns; then roll the tapes together same tape speed by some mechanism.

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