The “Standard” caliber 691 of the Fabrique d’Horlogerie de Fontainemelon bases on the common FHF caliber 69 and added a center second hand to it.
Since the available space is very low on these form movements, the FHF had to use an extraordinary solution: The fourth wheel indirectly drives a wheel on the top of the main plate, which itselfs drives the center second pinion.
The rest of the caliber 691 is identical to the FHF caliber 69.
|Size:||6 1/4 x 8'''|
|Number of jewels:||17|
Nickel anular balance|
|Balance bearing / direction hairspring:||Counterclockwise|
|Winding mechanism:||yoke winding system|
|Setting lever spring:||4 hole(s)|