The Hewlett-Packard Model 3410A AC Microvoltmeter is a tuneable phase locking voltmeter designed to measure ac voltages from 3 microvolts to 3 volts full scale. When tuned to any discrete frequency between 5 Hz and 600 kHz, the 3410A will indicate the amplitude of the signal present at that frequency, rejecting all noise and non-harmonically related signals. Two outputs are provided on the rear panel to extend the usefulness of the 3410A. The RECORDER OUT terminal provides a dc output that is proportional to meter deflection. This output, 1 V into 1 ki2 for full scale deflection, may be used to drive a pen recorder or other auxiliary equipment. A 5 V square wave at the tuned frequency, which may be used to drive an electronic counter for making precise frequency measurements, is available at the OSC OUT terminal.