Relay Calculating Engine is a machine that calculates square roots.

The frame of the relay computer can hold up to 30 identical relay modules, built using printed circuit boards. Each was designed to hold 16 relays for a total of 480 relays maximum. The display unit makes use of eight Russian IN-16 nixie tubes.

Computer is driven by mechanical clock pulse generator. This makes use of a motor driving a cam which presses alternately on two microswitches. Using this device I can generate regularly spaced pulses to sequence the machine through its various internal states during operation. The speed of the clock can be varied by the user so that they can watch carefully the sequence of lights corresponding to relays energizing when the machine is in operation.