The 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 ?V to 300 V full scale. Meter calibration responds to the absolute average value of the applied signal, calibrated in RMS Volts from 20Hz to 4MHz. The accuracy as a % of reading is ?4% (20 to 40Hz), ?2% (40 to 100Hz), ?1% (100Hz to 1MHz), ?2% (1 to 2MHz), ?4% (2 to 4MHz). Input impedance is 10 Mohms. The AC amplifier output is 1 V rms open circuit for full scale meter indication. Also avaliable is the HP 400F?it is the same great meter as the 400FL except for the calibration.