Circular logarithmic ruler "KL - 1" is designed to perform mathematical operations of multiplication, division, squaring, obtaining the square root, finding the trigonometric functions of sine, cosine, tangent, as well as inverse trigonometric functions, finding the area of ​​a circle. Manufacturer: Moscow Scientific and Industrial Plant of Control and Measuring Instruments "Kontrolprilad". The set includes a ruler, a box and instructions in Russian. The box and instructions are damaged.