H. Aron Type K Meter, Used by Budapest General Electric Company, 1903

Hermann Aron, a German physicist and lecturer-turned-manufacturer, developed a pendulum watt-hour meter in the 1880s for companies that supplied electricity to consumers in Europe's growing urban areas. Swinging pendulums turned hands on dials that accurately registered how much electricity customers used--so companies could charge appropriate rates. Aron's pendulum meters remained practical until less expensive motor meters became standard.