Let's take a quick break from disassembly to investigate the circuit board.

The yellow box is the power supply circuitry. It provides the three regulated and one unregulated rail used by the device.

The red box shows the high speed high voltage relays. These switch between ranges. They make a nice soft ping when they activate.

The orange section is the multiplexer, most function switching occurs here. The large white square is a high voltage precision matched resistor divider from Craddock

The blue and green boxes hold the -4.2V and -6.4V references respectively. The 6.4V zener (1N4579, shown in image 2) is small, orange and VERY expensive

The purple box shows the multi-slope integrator circuit. The white box is the integrating capacitor

Lastly, the black cylinder with four wires going to it is a special four-wire resistor used in precision current measurements.