+12VDC and -12VDC power supply. If either one is unstable, then the voltage output of the Pendulum Pot will be unstable. The +/-12VDC is generated inside the AV-3 Module and wired to the Pedestal through the GREY cable and eventually gets to the Pendulum Pot. The -12VDC is reduced to around -10VDC by the small blue trimpot on the PCB on the back of the Pedestal. That blue trimpot is adjusted to get the +60mVDC Plumb Voltage (output of the Pendulum Pot wiper) when the Pendulum is in the Plumb position.