Electron17 0 Posted August 26, 2014 beat at a certain speed? We see that a 21j has a beat rate of 21600 while an ETA beats at 28800. What makes a watch beat at a certain speed at start up? Why does, for example, an ETA not start beating at 21600 when it is started? May be a stupid question but would just like to know. Share this post Link to post Share on other sites
PhillyRock 0 Posted August 26, 2014 I believe it's the regulating fork. (The wishbone looking thing near the balance assembly) Some are further apart making the beat longer whereas others are closer creating a quicker catch and beat. (I fully realize that I'm probably not using proper terms and lingo but minus the technical stuff it's just what I assume in layman's terms) Share this post Link to post Share on other sites
black263 228 Posted August 26, 2014 The length of the pendulum determines the rate of tick of a clock. In a watch, the balance spring assembly replaces the pendulum, and has the same function. Springs are calibrated to run at specific number of "ticks" per second, and this determines the beats per minute, and per hour. So 8 beats per second is 28,800bph, 6 per second is 21,600bph. Share this post Link to post Share on other sites
