How do you know what the proper BPH is for any given watch?

Thanks

Ed

I am sure someone will come along with more info & a better statement but from what I understand some of the earlier pock watches were slow train which were 16200 beats per hour, then they went to 18000 BPH (5 BPS) which stayed that way until the late 1940's when watches started being made at 21600 BPH (6 BPS, today there are some that are 28000 (8BPS) & 36000 (10BPS).

It is my understanding that one reason they had remained at 18000 for so long was due to oil that was used but when synthetics were devloped they could up the beat.

There is a formula for determining the BPH but I have never tried it, it invloves counting the teeth on the wheels & leaves on the pinions. It is written as (EW x FW x TW x CW x 2)/ (EP x FP x TP x 60) so EW=escape wheel, FW=fourth wheel, TW=third wheel & CW= center wheel, the others EP etc are the pinion leaves for the corresponding wheel.

I am sure I made that as clear as mud.

Tom

Tom,

Thanks for your explanation on slow & fast trains.

Pete

Tom.
Thanks for the explaination on the differences. I didn't know when the 18000 BPH started and ended.
I imagine all my pw's fall in the 18000 BPH range.
If an old one shows around 16000 range on my watch timer I will know that it is a slow train.