The standard deviation computer is a small electronic analog device which is designed to calculate the standard deviation of a voltage signal with less than 5 per cent error. The output is a continuous voltage signal proportional to the standard deviation which is generated with a computation time equal to the sampling period. Mathematically, this instrument computes the mean absolute deviation which is related to the standard deviation by a constant factor. It accepts signals in the frequency range of from d-c to some upper limit determined by amplifier bandwidth over a wide range of amplitudes and computes with sampling times up to 3600 seconds or more. In field tests, the computer operated successfully on the output of a wind vane.