Watch beat

[Seiko97]

Hello watch enthusiasts! I have often wondered what makes some watches tick at 21,600 bph and others at 28,800 and so on. Does it have to do with how many teeth the escapement has? Or  does it have to do with a specific layout of the movement? This is something that really fascinates me and I would love to know how this works.

[Geo]

In simple terms the lower the mass of the balance the faster it will beat.  The hairspring also has to be matched to the balance mass to get the correct beats per minute.  

[JohnR725]

57 minutes ago, Geo said:

In simple terms the lower the mass of the balance the faster it will beat.  The hairspring also has to be matched to the balance mass to get the correct beats per minute.  

Geo  is correct the physical characteristics of the balance hairspring combination determine its rate of oscillation. Then the gear train ratio determines the rate at which the hands revolve. 

[Brian3]

Agree with above answers, length of the hairspring, I used a hairspring vibrating tool like this to vibrate my hairsprings at school, they were oversized and once you found the vibrating point you needed you cut the hairspring, then the fun part of introducing bends, pinning to the collet etc.........

[Seiko97]

Wow thanks for the answers fellas! That makes sense to me now. The funny thing is that I had a vintage Seiko 7005 given to me by my Grandfather and for whatever reason it was beating very smooth, smoother than a 7s26 and almost as smooth as an ETA 2824. Once I took it apart and put it back together it started to run normal at 21,600.... Very weird.