That difficulties in the use of various types of pressure gauges warrant meticulous scrutiny in the rendering of an accurate pressure‐time curve has advanced each type of gauge for particular work. In powder gas and internal combustion engine gas pressures the spring type and piezoelectric type offer great possibilities with the first a self‐contained unit and the latter a charge‐collecting device, and with the former following the true curve by an admitted time lag and the latter assumed to be responding instantaneously. Sparse comparative records of the two show the case to be more nearly the reverse of what the popular assumption leads one to believe. Fuller data are needed to determine the comparative lagging characteristics of both types.