Second hand on clock moves a step anti-clockwise?

Question

Does anyone else ever experience this? I do, once in a while, especially if I glance at the analogue clock on impulse. Would be really interesting if there's an explanation for this phenomenon...

Answer 1

Backlash (wear and/or clearance) in the gearing of the escapement. The escapment is a sprecial mechanism that allows the gear to move only one tooth position at a time based upon a rocking arm.  ( Look half way down the page of the attached link) As the rocking arm pivots the left and right stops alternately engange the sawtooth gear allowing ith ethe gear to advance slightly. This mechanism is also what is responsible for the classic Tic-Toc or ticking sound.

There is a saw tooth pattern for the escapent gear. As the right stop comes down and engages the saw tooth is scarpes and wears the base of the tooth.   If the stop arm is slightly long it will push the sawtooth backwards AND over time the impact of the right stop wears the base of the sawtooth. The added wear allows the second hand to travel slightly further. When this wear happens the left stop will strike the upperpart of the tooth and push it back slightly.     So the backward motion can be caused by either the left or right stop. New clocks will have unworn gears and slightly longer stops so as the clock ages the backwards movement  starts out with some, improves with time as parts wear in, then worsens and the wear shifts to the left stop with worn sawtooth bases.