Cal. 6497 and 6498 date to about 1950. They remain in production as of 2019 and are used as a basis for training in many watch schools and are decorated and developed into many complicated movements. The movements were originally produced by Unitas before it was fully integrated with ETA. They were updated to “-1” spec around 1967, and the ETA name was applied only around 2005.
Clones of the ETA 6498-1 include the Hangzhou 9310 and Sea-Gull ST3621.