The development of an instrument which measures the rate of respiration from breath to breath is discussed. The device uses as its input the impedance change of the chest cavity associated with respiration. It is designed to be part of the Physiograph system. The tachometer contains a trigger which produces a set of pulses corresponding to the points of maximum inspiration. The pulses control circuitry which measures time between the pulses. The time measurement is converted to a measure of rate that is linear within 5% from 5 to 100 breaths per minute. Included is a discussion of the effect of component drift in the switching circuitry. Also described is a method of obtaining linearization of the rate with an RC integrator using a non-linear resistor. Finally, the trigger, which undergoes transition when the impedance signal moves a set amount from the relative maxima or minima, is discussed. Records of the tachometer operation in the Physiograph system are included.