From the ETA 900 ebauche, modified balance. Other variations in the family included different bridge shapes and either Breguet or Flat Hairspring.
Manual wind, sub second
Dm= 23.35 mm, H= 3.5mm, F= 1.3mm, T= 1.7mm
18,000 a/H Frequency
41 hour Power Reserve
Mainspring: 1.55 x 9.0 x .10 x 290mm
Hands: 1.40, .80, .22
Specs courtesy Dr. Ranfft
I have a 15j 10BA with a 1944 date code.