About 1883 Gruen started to add to the good Swiss Aeby made movements with his 11-13j 18 size o.f. and hunter key wind and set. Continued with serial numbers for both at about 20k. I recently got a good example 23372 13j. Completely original with Muhr case and perfect dial.
Case may be brass? Keyhole perfectly aligned. Internally hinged glass to set. Very little surface wear. Please add here other low numbered ones 25k or less and descriptions. May not be the first Gruen designed model?
Added 13080 earlier 1879? Aeby example.