C10 KL1

During the 1960s, several manufacturers in the Soviet Union created the C10 KL1, a circular "pocket watch" slide rule with the same computing power as the contemporary Mannheim layout rules of the day.

C10 KL1

Type	Slide Rule (Circular)
Cost	3 Rubles, 10 Kopeks (approx. $3.00)
Calculator
Precision	2 to 3 significant digits
Display type	analogue scales, fixed index cursor and moveable needle
Programming
Other
Dimensions	5cm diameter, 2.1 cm thickness

Overview

The KL1 pocket rule was notable for its small size with comparatively powerful computational ability. Unlike most slide rules, which had scales run the length of the rule, circular slide rules like the KL1 have concentric rings of scales around the circumference of the face. This means that the power of a 5cm circular rule (approximately 2 inches) could achieve the same accuracy as a 15,6cm rule in only a third of the physical space. The KL1 was designed to be compact, rugged, and capable of one or two calculations in sequence quickly and fairly accurately. Instead of having multiple scales slide against one another, the KL1 uses a Gunter rule design, where a single scale is measured to a set distance, and that distance is transposed onto a new part of the scale. both faces have an index needle, fixed at 1 for the back face scales, and a measurement needle, which is aligned to match both sides together. Once the measurement needle is set, the entire front face can be rotated to place the measurement at a new starting point. This allows for several multiplications by the same multiplier to be done quite quickly. The manipulation of both the needle and the front face occur via two crowns on the side of the rule, which prevent outside forces from interfering with a measurement.

Scales

The KL1 is a duplex (two sided) rule with a total of five scales, arranged with two on the front face and three on the reverse face.

Layout

The layout of most circular slide rules is not standardized. The closest scale set to the KL1 is the Mannheim layout, but with heavy modification.

Front

A C

Rear

DI S ST/T

Transferring Between Scales

The KL1 has an unusual setup that invites for quick calculations of single multiplication or division, reciprocals, and using trig functions in calculations. Note that the rear face has an inverse scale as compared to the front face. The trig scales S, ST, and T are keyed to this scale, which aids in reading values without flipping the rule over, but means that when transferring from front to back (and vice versa), the reciprocal value is what is transferred. This can be remedied by using the inverse operation as desired (dividing when intending to multiply, etc) to get the needed result, but it is an extra step in calculation that must be remembered in contrast to traditional layouts.