A method is presented for instantaneously obtaining a numerical value proportional to the area of a recurring voltage transient. The underlying principle is the summation of pulses from a generator whose repetition rate is a linear function of the instantaneous input voltage. The technique allows accurate gating to reduce the effects of unwanted signal and noise and has a high order of stability and linearity. The particular device actually constructed and tested was designed to measure the area of the roughly triangular voltage change, about 1 msec in duration, produced by ventral root nerve fibers activated in a monosynaptic reflex.