6N

Start Year
1924
End Year
1926
Jewels
15, 16
bobbee
Posted August 14, 2014 - 3:10pm

Both have marks at the left upper edge of the detent screw, which is on the right of the crown when facing upright as in top pic.

Janet's example also has a larger circle to the right of the smaller ratchet wheel.

Reverend Rob
Posted August 14, 2014 - 5:52pm

Based on the Sonceboz 246. Modifications to the balance and cock by Bulova.