this tooth is as follows: at 45 minutes after the hour, the tooth pushes a small hook that protrudes into the hour wheel area. This hook will catch any falling hour leaf (as mentioned above, it falls from its metal tab a few minutes before the hour) until it is released by the minute leaf's fall at the top of the hour. Daylight saving time Many vintage digital clocks with split flap displays cannot be wound back, as the flip mechanism operates only in one direction. Instead they must be either wound forward 23 hours to achieve the effect of winding back 1 hour at the end of daylight saving time or the clock may be stopped (by disconnecting it from power) for 1 hour. However, on some newer clocks, forward and backward time setting is possible. GE clocks sometimes had this feature. Gallery See also Cifra 3 Digital sundial External links FlipClockFans.com - Flip Clock Aficionado Forum Clock designs