The Hammond organ is an electric organ, invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Various models were produced, which originally used tonewheels to generate sound via additive synthesis, where component waveform ratios are mixed by sliding switches called drawbars and imitate the pipe organ's registers. Around 2 million Hammond organs have been manufactured, and it has been described as one of the most successful organs ever. The organ is commonly used with, and associated with, the Leslie Speaker.