Odd bph watch movement?

[Jantje]

Hi all,

I am new to this forum, one of the reasons I opened an account is to ask you legends what's up with this watch I have here...
This is a 1917 AP ladies wristwatch, sadly converted to a pendant watch at some point in its existence.

Inside is a pretty 18 jl's movement, 18mm in diameter. It seems to run fine, amplitude is great even though some dirt can be seen too. 
Now the odd part, when placed in a timegrapher it detects 19800 bph tick rate, and then ++++, which was odd as the watch seemed to keep time before. I tried to slow it down as much as I could as I was convinced 19800 was the right beat rate and the watch was running fast. After adjusting the regulator the timegrapher showed +700 more or less. That is when I tried to check timekeeping again by setting the time right, after a while it was obvious the watch was running slow. I would have expected this movement to have a beat rate of 18000 and now things were getting more and more odd... Decided to count the teeth of all the gears (is this the right/easiest way to find out what beat-rate a movement must have?). 

Center wheel: 56 teeth
2nd wheel: 52 teeth (receiving center wheel with 6 teeth, all of the other gears apart from the center wheel were receiving the previous gear with 6 teeth)
'seconds' wheel 50 teeth
Escape wheel 15 teeth

would this calculation be correct?:
1 turn of the center wheel gives 9.333 turns of the 2nd wheel
9,333X8,666 gives the amount of turns of the seconds wheel
80,888 X 8,333 gives the amount of turns of the escapewheel: 674,07
that times 15 and then times 2 for the pallet fork gives 20222 bph?

Never done this before but the amount seems to be more or less correct.
If this is indeed correct, how would one proceed to time this movement? are there timegraphers where you can manually adjust the bph to a custom number?
Hope to hear from you, also wondering if you are familiar with these odd bph movements. 

Jan 

[ColdWind]

If the number of teeth of wheels and leaves of pinions you had counted is right then yes, the bph is 20222, which is odd but it does exist, for example Cal 104 from Jaeger-LeCoultre is also 20222 bph.

So to time the movement what type of timegrapher do you have? If you have the Weishi No. 1000 then in automatic selection mode it will display the closest beat number, but the test result is not correct. The following beat numbers are selected by automatic selection mode: 12000、14400、18000、19800、21600、25200、28800、36000、43200. In this case the timegrapher would automatic select 19800 because it is closer to 20222 than 21600. You need to select the beat manually in Manual selection mode, which will let you choose 20222 bph, before timing the movement. Manual selection can selected out the beat number that Automatic select can not identify and rare beat number.
The following beat are selected by Manual selection mode:
3600、6000、7200、7380、7440、7800、9000、9100、10800、11880、12000、12342、12480、12600、13320、13440、13500、14000、14040、14160、14200、14280、
14400、14520、14580、14760、14850、15000、15360、15600、16200、16320、16800、17196、17258、17280、17786、17897、18000、18049、18514、19332、19440、19800、20160、20222、20944、21000、21031、21306、21600、25200、28800、32400、36000、43200

Edited December 20, 2022 by ColdWind

[praezis]

Your calculation is correct, but don't neglect the decimals: 20222,22... It matters for a few seconds difference. (I correct: about 1/2 sec. )

If you look into beat rate tables, you will find 20222 exists.

Frank

 

Edited December 20, 2022 by praezis

[nickelsilver]

I've worked on a number of 20222 pieces, LeCoultre, that AP was probably made by LeCoultre. They did some 20944 too.