Vintage Soviet Circular Slide Rule KL-1 USSR Engineering Calculator Logarithmic Scale Vintage circular slide rule KL-1, manufactured in the USSR. This mechanical calculating instrument was widely used by engineers, technicians, students of technical universities, and scientists before electronic calculators became common. Circular slide rules like the KL-1 were designed for performing logarithmic calculations, multiplication, division, square roots, percentages and other engineering operations. Such devices were commonly used in technical institutes, research laboratories, aviation engineering, and industrial design offices throughout the Soviet Union during the mid-20th century. The circular design allows faster and more compact calculations compared to traditional straight slide rules. Condition: Pre-owned vintage condition. The instrument shows signs of age and use. Dial and scales are well preserved and readable. Please see photos for detailed condition. Details: • Model: KL-1 • Type: Circular slide rule • Origin: USSR • Material: Metal body with printed logarithmic scales • Diameter: approx. 8 cm (3.15 inches) • Included: ruler, plastic box, instructions for use (paper is damaged in some places) A great collectible for scientific instrument collectors, engineers, mathematicians, or vintage technology enthusiasts.