C19 Soviet KL-1 Slide Rule Watch

This is one of the most curious items in my collection: a pocket size watch slide rule. This two inches diameter circular slide rule or Model KL-1, was manufactured by the Technical and Lights Company "Sunrise", in the old Soviet Union. These watch type circular slide rule was fabricated by different companies from 1918 to possibly 1978. T The manufacturer's logo is on the rules front face. There is nothing else on the rule itself that allow to determine the manufacturing year.

The KL-1 is a double sided circular slide rule with two rotating "hairlines". There are a double log (outer) and a single log (inner) standard scales paired on the front face [ A - C ]}. On the back face a single standard log scale (outer) paired with two inner concentric scales: a circular sine scale and a long spiral tangent scale [ C - S - T ] . These trigonometric scales are divided in degrees-minutes. Only the front disk can be rotated with one of the a knurled knobs, the disc with the trigonometric scales does not move. The second knob rotates the two hairlines; these are aligned and point to opposite directions. On the crystal covering the front disk there is engraved a reference line aligned with one of the knobs.

Click on the next link to see professional panoramic pictures of the C19 KL-1

https://www.sliderulemuseum.com/Circular/C19_Soviet_KL-1_PocketWatch.jpg