|DC voltmeter circuit using a milliammeter (A) in
series with a high resistance (Rs). If the resistance
of the ammeter is known and the combined resistance of Rs
and A is large compared with the resistance in the circuit under test,
the ammeter reading allows a good estimate of the test voltage (Vt)
to be made. For a particular ammeter-series resistance combination,
the meter can be calibrated directly in volts.