Sapphire Instruments SI-9101 Calibration Procedure page 7

3.5 High Frequency CMRR adjustment
a. Referring to Fig. 11, connect output BNC to the oscilloscope has good grounding.
b. Connect both input lines to a 155 Vp-p, 20 kHz, sine wave signal source.
c. Put SW1 at 1/10.
d. Set VOLTS/DIV switch on oscilloscope's panel to 2 mV and the TIME/DIV switch to 0.1ms.
e. Adjust VC1 slightly to make the amplitude of displayed waveform as small as possible.
Finally the amplitude should be less than 28 mVp-p (after excluding noise).
3.6 Repeat 3.2 and 3.5 adjustment until both adjustments are O.K.
Fig. 11
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