Soviet Slide Rule

This circular slide rule is markedly different in almost every respect from the usual slide rules manufactured in the Soviet Union. Instead of being "just good enough", and generally lacking in any non-functional attributes, this thing is overbuilt, rugged, and pays great attention to both function and beauty.

It weighs over a pound, is almost 9" in diameter, and can multiply, divide, take sines and tangents, and inverse sines and tangents -- all accurate to 3 or 4 decimal places. Almost certainly it is a military slide rule, probably associated with artillery (calculating the elevation of the gun to aim it is a fairly involved exercise in mathematics).

You can read more about it here.