KL-1 (КЛ-1) circular slide rule, an iconic Soviet calculating instrument produced since the 1960s. It resembles a classic pocket watch or stopwatch. Key Features: Purpose: Analog engineering calculator used for multiplication, division, squaring, and calculating trigonometric and logarithmic functions. Design: It has a housing with two knobs (crowns) to control the inner dial and two hands (a black, movable one and a red, stationary one). Reversibility: The device is double-sided. The side shown in the photo contains basic scales (multiplication/division, squares), while the other side is typically used for trigonometric calculations (sines, tangents). Manufacturer: Made in the USSR; the dial features a stylized manufacturer's logo, stylized as "МАТЕМА" or a reference to precision factories. Condition: New, never used, in original box with instructions. When purchasing more than one item, you pay shipping once.