HP/ Agilent 334A Distortion Analyzer 

5 Hz to 600 kHz Range
Measures Total Harmonic Distortion Down to 0.1% Full Scale
Residual Noise Below 25
Voltage Measurement Over a Range 300 to 300
V RMS Full Scale
Auto Nulling Feature
AM Detector

HP model 334A Distortion Analyzer measures total distortion down to 0.1% full scale at any frequency between 5 Hz and 600 kHz, hamronics are indicated up to 3MHz Noise levels as low as 25 microvolts can be measured. The HP 334A includes automatic fundamental nulling and amplitude modulation detector.