Every DC power supply in Bottlehead equipment could be monitored, both high voltage and heater current. They shouldn't change. They also can not be adjusted. But the meter looks cool.
Way too much information about amp meters:
There are three kinds of current meters, one with a shunt, one without a shunt (it is internal) and industrial current meters with current transformers (never mind those).
Meters never have circuit current through the movement. The movement is a voltage meter.
A meter that has an external shunt will have something like "100mV=FS" on it. That means full scale on the meter is 100mV. A shunt is a precision resistor that produces a predictable voltage at a specific current. For example 100mV for 1000A DC. I have seen these.
Those that don't use an external shunt have the current, much lower current, going into and out of the meter. They can measure AC or DC, the AC is rectified because the meter movement is DC. These meters have internal precision resistors that the volt meter, movement, reads across. An example is the meter you pictured above. It doesn't have 10A going through the meter movement but doesn't have a volt/full scale marking on it either.
