The release of the mechanical back up reserve mechanism in case of a power cut.<br />In this type KYA 1 clock from Landis & Gyr this happens every 2 hours and 3 minutes.<br />The synchronous motor drives the dial directly but also winds up a spring in a drum which has an overwind slip clutch in it.<br />To avoid a mechanism sticking over a long period ( no power cuts ) the back up reserve is forced to release by means of a couple of levers within the clock work mechanism. A brief hum is heard when the magnetic lock is moved sideways and the ticking of the escapement.<br /><br />This clock is about 35 to 40 years old and still works well, can't be said from those battery operated plastic clocks which are sold now these days<br /><br />I created this video with the YouTube Video Editor (http://www.youtube.com/editor)
