I just finished servicing a very nice original Heuer with a very early R72 movement. The owners father passed away last year and he wanted to have it restored and also find out its age. There was no documentation with the watch. This is the earliest R72 that I have ever seen. The cal ref # is stamped on the top plate instead of under the balance bridge seen on most of these movements. The serial number is 57706. Anyone know the age? Any other info welcome. Thanks