This instrument was designed to make a graphical record of small speed variations in any sound recorder capable of producing a millivolt output at about 1000 c.p.s. It consists of the following sequence of components: amplifier→clipper→bandpass filter→frequency discriminator→demodulator→oscillograph. The clipper eliminates amplitude variations and the filter passes only the fundamental frequency of the clipped wave. The discriminator is a parallelTequivalent of a Wien bridge balanced near the upper cut‐off frequency of the filter. The oscillograph is a model BL‐201 direct‐inking instrument made by the Brush Development Co. Over‐all calibration of the wow meter is accomplished by an RC oscillator and calibrating switch which changes the oscillator frequency 1 percent. Preliminary estimates and tests indicate that speed variations of less than 0.1 percent can be measured reliably if these variations occur between12and 100 per second.