Abacus with each counter held in position by friction or magnetic attraction

An abacus for performing calculations by sliding counters along partition walls extending vertically. Each counter has a spherical or beadlike head protruding above the body of the abacus, as well as a stem. Shafts extend horizontally through the partition walls and also through the stems of the counters. A hole is formed in each stem of the counters and horizontally extends partially through the stem. A compressed spring is mounted in each hole, and a small ball is attached to the front end of the spring. The side surface of each counter which is not in contact with the ball is pressed against the opposed partition wall by the action of the spring. Thus, the counters are maintained at their present positions even in a moving vehicle.