The problem of stopping a moving light‐beam on the edge of a phototube without any tendency to oscillate or ``hunt,'' and with speed and precision has been solved by a new method and a recording potentiometer is rapidly and accurately balanced. By (1) artificially canceling the generated back e.m.f. of the moving galvanometer thus advancing its return movement from a deflected position, and (2) delaying the grid potential change of a triode amplifier in the photoelectric circuit, galvanometer lag is counteracted and the potentiometer is balanced with an accuracy of a few hundredths of a percent of the range. The total power input to the instrument is about 35 watts and the contact carriage speed is made as high as 10″ in 20 seconds.1The fundamentals of the complete instrument are discussed and equations describing the galvanometer movement are included.