Once designers exhausted the various flat, straight and round versions, and applied them to everything from lighters to tie tacks, you might think there was no fresh ground left to cover, but not so. Cylindrical rules were made by Otis King, and a bizarre multi-scale rotating rule was made by Thacher, and later sold through K+E (Note: we are indebted to Bob Otnes of the Oughred Society for pointing out that while the inventor's name was Thacher, early units have a typo on the engraved nameplate, and say 'Thatcher'). Modern designers even made pencil holder slide rules with rotating cylinder sides.

In another section we showed giant rules for classroom instruction, but some crafty engineers decided the demonstration solution could be achieved by using transparent slide rules, and an overhead projector, allowing the teacher to manipulate the rule more easily. This technique required a dark room, making note taking, and the student's personal rule setting a bit awkward. K+E, Pickett and Aristo all made these fascinating projection rules.

The top tube with its spiral scale pulls out and rotates, the black cursor sleeve rotates and moves up and down, and the chrome handle, attached to another spiral scale is held stationary. There are several versions of this rule and scale set.

* 2 working scales.

Visit Dick Lyon's 'Otis King's Patent Calculator' Pages

Learn about one of the most unusual slide rules.

The 18 inch scales have two portions, one external segmented cylinder that rotates, and a moveable internal cylinder that also rotates. The scales achieve very high accuracy due to their equivalent length of 30 feet. This permits answers to 4 or sometimes 5 decimal places, which is extraordinary. Operations are multiplication, division, squares and square roots.

The 4013 had an accessory sliding magnifier to allow even finer setting of the scales, but is otherwise identical to the 4012.

Concise made several variations of this basic rule, with impedance nomograms, and other special purpose scales and data for other professions.