Admin do you remember if there was both a triangle and a "chevron or arrow" on this 1926 17j 10AN movement?
There is an arrow below the serial number Will, and it says "triangle" date mark.
I do see the arrow in this closeup snippet.
...but owner emailed me a couple years back confirming the case SN starts with an "8". Admin knows owner, and probably checked this watch out in person.
So could this movement have started out life as a 1st 5K?