Remember this is Line Voltage and can be deadly if not done safely. This uses fixed resistors to make AC voltmeter range of 1 mV = 1Watt to check a purely resistive load.
All .47 ohm shunt resistors have 5 Watt power rating. Other resistors can be .5 Watt rating.
Vary Wattage of lamp and watch reading on millivolt scale.
