Kontrolpribor

KL-1

I see lots and lots of these on eBay, mostly selling for around $40 and coming from various parts of the old Soviet Union. This one appears to date to 1966 and the faces are clear plastic. I think they were made for quite a while starting in WWII, and maybe the older ones are glass. If anybody knows please send me a note.

One side (left) bears an outer A scale and an inner C scale, both mounted on a disk that can be turned with one of the knobs. The plastic "glass" on that side has a fixed hairline right under the knob that turns the disk. The other side (right) has a fixed disk bearing an outer C scale and inner S and T scales. The other knob turns the pointer simultaneously on both sides.

If things are properly aligned, when the pointer is positioned to the index of the fixed-dial size, the pointer on the rotating-disk side points to the fixed hairline. (I had to take the "glass" off one side and slightly bend the pointer to achieve this alignment.) That means both multiplication and division can be done with two operations. Start by setting the pointer on the fixed-disk side to either the multiplicand or to the divisor on the outer C scale. Then turn the instrument over to the rotating-disk side. If multiplying, rotate the disk so the other multiplicand, on the inner C scale is under the pointer, and the product will then be under the fixed hairline on the C scale. If dividing, rotate the dial to bring the dividend, again on the inner C scale, under the fixed hairline and the quotient will be under the pointer on the C scale.