Routine calibration of an accelerometer is performed by comparing the open circuit voltage output of the unknown with the output of a laboratory standard which has been calibrated as described in the previous two papers. This comparison is performed with both accelerometers excited simultaneously in a special double‐ended vibration exciter. The construction of the special vibration exciter and the precautions taken to ensure that both accelerometers are exposed to the same vibration are described. The double‐ended vibration exciter is also used in part of the reciprocity calibration of laboratory standard accelerometer.