The Keysight / Agilent / HP 400FL AC Voltmeter is primarily intended as a dB Meter, however it can indicate both V and dB. The meter has a linear dB scale with a logarithmic AC scale below.

The voltage range is 100 uV to 300 V full scale. Meter calibration responds to the absolute average value of the applied signal, calibrated in RMS Volts from 20 Hz to 4 MHz.

The accuracy as a % of reading is 4% (20 to 40 Hz), 2% (40 to 100 Hz), 1% (100 Hz to 1 MHz), 2% (1 to 2 MHz), 4% (2 to 4 MHz).

Input impedance is 10 Mohms. The AC amplifier output is 1 V rms open circuit for full scale meter indication.