The paper gives specific design data of two known types of pressure-recorders. They were designed for the hazardous conditions associated with the short-circuit testing of circuit breakers, and where the quantities recorded could be readily correlated with all the other physical quantities involved in such tests. Typical investigation problems and data on circuit-breaker development are given, and serve to illustrate the importance of these measuring and recording instruments.The measurement of dynamic strain by resistance-wire strain gauges is also considered, together with the technique adopted for recording dynamic strain phenomena. A typical measurement taken on a circuit-breaker mechanism is analysed.