Westinghouse Type A Polyphase Wattmeter, 1903-1906

In the late 1800s, companies that supplied electricity to consumers needed a way to measure how much customers used -- and then charge them accordingly. Paul McGahan, a Westinghouse electrical engineer created a practical polyphase wattmeter in 1899 to measure electric power usage. This design was adopted by other companies and remained a standard well into the mid-1900s.