Electricity meter, c 1930.
© Science Museum / Science & Society Picture Library
A 'Type H' single phase service meter based on the electromagnetic induction principle. Inside this meter is a spinning plate moved by electromagnetic induction, which is geared to a series of dials that register the amount of electricity used, based on how much the plate rotates. It shows the amount of electricity used in kilowatt-hours (1000 watts of power for one hour of time).