[Dekatron]

The circuit for the Mk III is almost identical to the CT160, the only differences are in the component values chosen around the mA/V potentiometer and the addition of the step-values for the Grid volts potentiometer. R7-R14 form a voltage divider chain where the potentiometer RV5 with in parallel R15 is inserted at different steps so that it adds the step voltage to the variable voltage. In the mA/V circuit a few resistors, R3-R6, has been added to adjust the scale of the mA/V to make it fit.

I made a simple schematic by just cutting out the portions not needed for the SET AC position, note that the "Meter Switch" is set in the 100mA position to make sure that the common ground is set correctly, that the "Leakage" switch is set in the SET AC position so that there is a connection between H- (10) and the Meter connection (9) in the circuit in this position so that it forms a complete circuit for the current to flow.

You can of course redraw this even more but I usually use the circuit diagram as a base for these when checking an instrument as it is somewhat easier in my opinion as you can see where the wires and components are compared to the full circuit. The includd PDF-file contains the complete circuit diagram as well as the simplified with the cutouts and you can switch between them on the screen to compare them easily.