To measure the current through a shunt resistor, an ohmmeter or multimeter should be used. The following steps can be followed:

1. Turn off the circuit to be measured and connect the leads of the ammeter to the ports that have not yet been measured.

2. Connect the two leads of the ohmmeter to either end of the shunt resistor.

3. Connect the leads of the ammeter to the two leads of the ohmmeter.

4. Turn on the circuit and record the readings of both the ammeter and ohmmeter.

5. Connect an adjustable resistor to both ends of the shunt resistor and gradually adjust the resistance until the reading on the ohmmeter reaches the maximum value.

6. Calculate the actual current using the reading of the ohmmeter.

It should be noted that appropriate meters should be selected for measuring the current through a shunt resistor and both the source voltage and current should be within the measurement range of the meters to avoid damage.