Calibrating a Voltmeter using a Potentiometer is as follows:

• Connect the potentiometer to a power source and adjust its resistance to produce a known voltage.
• Connect the voltmeter in parallel with the potentiometer, so that it measures the voltage across the potentiometer.
• Compare the reading of the voltmeter with the known voltage, and if necessary, adjust the voltmeter's sensitivity until it gives a correct reading. This can be done by adjusting the internal resistance of the voltmeter or by using a multiplier resistor.
• Repeat the procedure for different values of voltage to ensure the voltmeter is calibrated over its entire range.

Calibrating an Ammeter using a Potentiometer is as follows:

• Connect the potentiometer to a power source and adjust its resistance to produce a known voltage.
• Connect the ammeter in series with the potentiometer, so that it measures the current flowing through the potentiometer.
• Adjust the ammeter's sensitivity until it gives a correct reading of the current. This can be done by adjusting the ammeter's internal resistance or by using a shunt resistor.
• Repeat the procedure for different values of current to ensure the ammeter is calibrated over its entire range.