The lever, also termed 'regulator', which alters the effective length of the balance spring in a clock, allowing alterations in the rate to be made by the clock's owner. The best clocks are free sprung, no index being used, as the effectiveness of costly escapement adjustments is reduced by altering the effective length of the balance spring. Rate adjustments in free-sprung clocks may be made by alterations to the balance, using movable weights or screws.