Circular slide rule

This is a rudimentary circular slide rule; only whole numbers are marked, and no smaller subdivisions.

Unless you have moved the points, it is set to show 2x3:
Move point B so that 2 on the outer ring is aligned with 1 on the inner ring.
Move point D so that the hairline is aligned with 3 on the inner ring.
Read off the product under the hairline on the outer ring.

Susan Addington, Created with GeoGebra

Quadrivium

Applets