We used to run on our tower clocks using a zero crossing circuit for time keeping- but stopped after we had a problems at a couple of theme parks - their none-zero crossing dimmers were putting a large amount of switching noise on the mains causing the timer to run fast. We have gone to an on board TXO. We also used synchronous motors to directly run our tower clocks - but now just minute impulse. Thomas D. Erb o: 508-359-9684 p: 508-359-4396 x 1700 f: 508-359-4482 a: 97 West Street, Medfield, MA 02052 USA e:  tde@electrictime.com w: www.electrictime.com