Before revision: Types Traditional analogue clocks Traditional mechanical alarm clocks have one or two bells that ring by means of a mainspring that powers a gear to quickly move a hammer back and forth between the two bells or between the internal sides of a single bell.
After revision: ,Types Traditional analogue clocks Traditional mechanical alarm clocks have one or two bells that ring by means of a mainspring that powers a gear to quickly move a hammer back and forth between the two bells or between the internal sides of a single bell.