Schiller AT-102 Service Handbook page 107

AT-102 ECG Service Handbook
ECG Amplifier Reference voltage
Switch the unit on and measure the voltage difference between the +2V reference
and the -2V reference on pins 1 and 7 of operational amplifier U79. Adjust trimmer
VR1 to achieve a voltage difference of 4000 mV ±2mV.
Reassemble the unit as detailed in Chapter 4. Re-check the voltage by again
obtaining a service printout (see following).
Article Number 2. 540 028
SCHILLER AG 2002
Section 5
Adjustments
5.11