Siemens & Halske Duncan Type A Wattmeter, 1899-1900

In the late 1800s, companies that supplied electricity to consumers developed wattmeters to measure how much power customers used so they could charge appropriate usage rates. Thomas Duncan created wattmeters bearing his name for several companies in the late 1890s. Duncan worked for the American branch of the German company Siemens & Halske beginning in 1899 before starting his own meter manufacturing business in 1901.