Pioneering work on electrical discharge machining was carried out in 1943 during World War II by two Russian scientists, B.R. and N.I. Lazarenko at the Moscow University (Lazarenko, 1943). The destructive effect of an electrical discharge was channelised and a controlled process for machining materials was developed. The RC (resistance–capacitance) relaxation circuit was introduced in 1950s, which provided the first consistent dependable control of pulse times and also a simple servo control circuit to automatically find and hold a given gap between the electrode (tool) and the workpiece. The RC circuit was widely used in the 1950s and later served as the model for successive developments in EDM technology.