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Created: 2001-11-24

Circular rules
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Concise circular rules are still in production and can be purchased at stores in Japan.
 Single sided plastic rule with diameter of 85mm.
 Scales are D [C, CI, A, K]. Back side has a compliment of unit conversion tables including weight, length, area, volume, temperature, pressure and energy. In case you are wondering, black material in the photo is the plastic bag for the rule.
 This model has Log Log and trig scales. Diameter of 110mm and equipped with rotating disks on both sides.
Scales are, front: K, A, D [C, CI, B, L], back: LL3, LL2, D [C, S, T1, T2, ST], total of 15 scales.
 This model is two sided with diameter of 110mm. In addition to a set of common scales, this rule has unique set of scales. They include, perpetual calendar, unit conversion, day calculation, age calculation, conversion between Japanese year and Gregorian year. Perhaps those scales are useful only for Japanese.
Pickett 101C

Circular rule from Pickett. It has no rotating disc, but equipped with double cursors (or indicators). Here is how to use it. Scales are, front: C, CI, A, Ar, L, Fa, LL2, LL1, DS, DT, M rear: C, S, ST, T, total of 15.
Gilson Midget

Gilson's 4 inch "Midget" circular rule. Gilson manufactured circular rules for many companies. In those cases rules are shipped without manufacturer's name on them. In addition to the standard scales, Gilson's rule has many special scales such as, fraction<>decimal conversion, drill sizes. This rule has total of 20 scales.
front: C, CI, L, A, Binary, LL, fract, Drill, Thread, MM,
back: 3 sets degrees, sines, tans, fract/decimals.
Gilson also produced a "big brother" to this slide rule. It is called Binary and measures 8 inches in diameter.

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