Note: In Fig. 26.16a, ammeter A reads the current I in the resistor R. Voltmeter V, however, reads the sum of the potential difference Vab across the resistor and the potential difference Vbc across the ammeter. If we transfer the voltmeter terminal from c to b, as in Fig. 26.16b, then the voltmeter reads the potential difference Vab correctly, but the ammeter now reads the sum of the current I in the resistor and the current IV in the voltmeter. Either way, we have to correct the reading of one instrument or the other unless the corrections are small enough to be negligible.