Maintaining power

Device for keeping a mechanical clock working while it is being wound In horology, a maintaining power is a mechanism for keeping a clock or watch going while it is being wound. Huygens Wound stateUnwound stateHuygens's mechanism Huygens' maintaining power in use The weight drive used by Christiaan Huygens in his early clocks acts as a maintaining power. In this layout, the weight which drives the clock is carried on a pulley and the cord (or chain) supporting the weight is wrapped around the main driving wheel on one side and the rewinding wheel on the other. The chain then loops down from the rewinding wheel and up again to the main driving wheel via a second pulley carrying a small tensioning weight which ensures the loop stays taut and the chain engages well with the main driving wheel and rewinding wheel. In the first illustration the clock is fully wound, the driving weight is up and the tensioning weight down, a ratchet on the winding wheel prevents it from turning back. The driving weight pulls the main wheel in the direction of the arrow. In the second illustration the driving weight has reached its lowest point and the tensioning weight is now up, the clock needs to be wo