An increased availability of high-precision a-c and d-c power sources has allowed routine electrical measurements to be made in the field with a precision previously possible only in the standards laboratory. Ac-dc comparisons are being made on the basis of the peak, rms, and average value of the sine wave source. The peak ac-dc voltage comparator described in this report was developed for use in the * standards laboratory to help meet the increasing demand for the certification of new field instruments.The described instrument is capable of establishing the ac-dc error of other peak comparators at frequencies from 50 to 2400 Hz with an imprecision of less than 15 ppm. (Author).