How the shunt works

The shunt is actually a resistor with a small resistance. When a DC current is passed, a voltage drop is generated for the DC current meter to display;

The DC ammeter is actually a voltmeter with a full scale value of 75mV;

The DC ammeter and the shunt are used together;

For example, the shunt resistance of the 100A ammeter is 0.00075 ohms;

That is 100A*0.00075 ohm=75mV;

The shunt resistance of the 50A ammeter is 0.0015 ohms;

50A*0.0015 ohms = 75mV.