Westinghouse Type A Wattmeter, 1903-1904

In the late 1800s, companies that supplied electricity to consumers needed a way to measure how much customers used -- and then charge them accordingly. Inventive electrical engineers developed various methods to measure electric power. Induction meters that employed magnetic fields to rotate a disc or cylinder to register energy usage would become the standard. Continued improvements made these wattmeters more compact and reliable.