Junghans AT-cut 4 Mhz movement(s) (and some of what came before)

The Junghans 667.26 is a 4 Mhz caliber that has been discussed here before:
1. When found in Doensen's book published 2006
2. A dedicated thread in 2014 by @sekunde
3. A…

Junghans AT-cut 4 Mhz movement(s) (and some of what came before)