This 6 volt battery powered unit could be used either as a continuous wave oscillator for receiver calibration,
or as a heterodyne wavemeter for transmitter calibration. Its frequency range is 120kc/s to 1Mc/s (wavelength
of 2500 to 300 metres). It was first calibrated in 1921. This unit is Serial No. 1352
Sec/Ref 3D/40