The Type 716-P4 Guard Circuit (Figure 1) is designed primarily as an accessory to the Type 716 -C Capacitance Bridge to permit three -terminal measurement of capacitance up to 1100 pF. It is especially useful for two- and three-terminal measurements over wide temperature and humidity ranges where the unknown must be kept in a conditioning chamber. Since the guard circuit eliminates the effects of the leads from the bridge to the unknown, the accuracy of measurement is the same as if the unknown were placed directly at the bridge terminals.