A comparison was made between hydraulic and electrical determination of the frequency response of two types of electromagnetic flowmeter. The output of the square-wave meter tested was reduced in amplitude by 10% at 7 cycles/sec; it lagged behind the input by approximately 4.5°/cycle per second. The output of the gated sine-wave meter was reduced by 10% at 24 cycles/sec and the phase lag was approximately 2.2°/cycle per second. No significant difference was detected between the results of either method of calibration. The frequency response of these instruments is determined by the characteristics of their electrical circuits. It is recommended that each user calibrate his own instrument; a simple method of electrical calibration is described. Since the frequency response of either meter is relatively poor, flow records obtained with them must be appropriately corrected. methods of calibration Submitted on March 9, 1964