Make your own circular slide rule

The slide rule is a simple but elegant mechanical calculator. A practiced user with a good quality slide rule can multiply, divide, exponentiate, take logarithms and perform trigonometric operations to three significant figures more quickly than with an electronic calculator. Below you will find a PostScript template and instructions for building your own pocket-sized circular slide rule, like the one pictured at left.

Templates and instructions

There are two files. Each is designed to be printed on a single 8.5 x 11 inch page at minimum 600 dpi resolution. The directions are in HTML.

• Template part 1 [PostScript] [PDF]
• Template part 2 - print to transparency [PostScript] [PDF]
• Building the slide rule (HTML)
• How to use a slide rule (from The Museum of HP Calculators)
• My source code (in C), used to generate the PostScript template.

This circular slide rule has the most essential functions of a scientific calculator. There are enough scales to let you do just about anything, but some things (like hyperbolic functions or tangents) require multiple steps. Think of it as a RISC processor!

• Side 1:
  • A pair of logarithmic scales for multiplication and division
  • An inner scale that runs from 0.1 to pi/2 radians, corresponding to the arc-sine of the inner log scale. For angles less than 0.1 radians, sin(x) = x to 0.16% or better.
  • With an extra step or two, you can get cosines and tangents.
• Side2:
  • The inner two scales are a continuous log-log scale, running from 1.105 to 22,000. Used with the outer log scale, these allow exponentiation and logarithms with arbitrary bases.
  • Numbers smaller than one can be handled by taking the inverse of the number, exponentiating, and taking the inverse again.
• The outer scale on Side 1 is 1/ the outer scale on Side 2, which makes inverting fractions a snap.

You may freely share the templates and instructions, as long as you don't charge anyone for it or bundle it with merchandise for sale. Please keep the copyright notice intact.

What next?

If you enjoy using my simple circular slide rule, you will probably find even greater enjoyment using a professional quality instrument. I have a classic Keuffel & Esser Log Log Duplex Decitrig given to me by my wife's uncle, and It is a real treasure. If you are very fortunate, you may have such an uncle. Or perhaps you can find a slide rule in an attic or at a garage sale. Good slide rules like the K+E operate very smoothly, are quick to use, and typically last for many years. Sophisticated models have more scales than my simple circular slide rule, making for greater flexibility.

Here are some favorite slide rule websites:

• An historical introduction to slide rules (from The Museum of HP Calculators)
• A short essay on Napier's bones
• The amazing UniVirtual interactive Java slide rule
• The Slide Rule Universe, an excellent source of information and a marketplace for new (yes, new) & used slide rules
• Slide rule links at dmoz