Errors in wattmeter:
i) pc - inductance: Pressure coil inductance causes wattmeter to read more power than actual .
ii) pc-capacitance: The wattmeter reads less power.
iii) Mutual inductance: An emf induced in pressure coil due to current through the current coil. This emf of pressure coil opposes applied voltage.
iv) Connection: In uncompensated wattmeter , the reading of wattmeter includes the powerloss in coils.