BALL Manufacture Caliber 7309
Swiss made mechanical movement
https://www.ballwatch.com/global/1/technology/movement---41.html

Dimensions: O 34.24mm, height 5.16mm
Functions: Hours, minutes, sweep seconds and date
Winding: Automatic
Vibrations: 28,800vph, 4Hz
Power reserve: 80 hours
Jewels: 25

--
Engineer M Challenger: our first chronometer manufacture caliber
https://www.youtube.com/watch?v=lJmAVJU5gVQ

8振動で80時間パワーリザーブは良いけどデカい香箱で直径が決まって残りスッカスカ…
https://static.watchtime.com/wp-content/uploads/2018/01/Ball_Watch_Caliber_7309_1000.jpg

ってまあ見えなきゃええか