A single‐channel analyzer has been built for measuring the pulse spectrum from proportional and scintillation counters; it counts the number of pulses whose heights lie betweenEandE+&Dgr;E. The interval &Dgr;Eor ``window width'' is constant within ±1.2 percent for all values ofEbetween zero and ninety volts. Curves are presented which show that the analyzer performs satisfactorily on the random distribution of pulse amplitudes obtained from counters.