How was the standards for chronometer certified omega watches in the 60s? Was it any different than today's cosc standard of -4 sec to +6 sec? Or the Meta standards?
Has always been +4/-6, though Omega service manuals say vintage movements (like a 561/751/etc) only need to be regulated within -25/+30. But the movements, when properly serviced, are still perfectly capable of holding COSC standards.