In reply to Henry Averill.

Normally, that would be the case - however, to convert beats to hz for a watch movement, you need to take half the beat rate since the beat is the number of times the pallet is tipped (two per cycle - since the balance trips the pallet twice per oscillation: once clockwise, once counter-clockwise). Therefore, the balance wheel of a 21,600bph movement will make 3 complete cycles in each second (3hz).

Hope this helps clarify!