Well i have the great privilege to be able to play with this one today. A fantastic 1665 Comex, 2nd series.... directly from the original diver. And what a sexy beast it is in front of the camera. Check the dial. See the 2000ft=600m ? Only on Comex my friends. You only see this dial on Comex watches. All the red and white 1665 have 610mtr (except the earliest ones of course). This one has a great case and perfect dial. The engraving is magical. 2nd series means, it's within the 1665 isuue-numbers above 2100. 2000-2100 is first series. And super rare. The 600 dial was only made for Comex. There are also 610 mtr Comex dials, but they where only used in the last batch or as replacement dial for damaged 600 dials later on. A lot of the great missions from Comex history and world rekord dives where archived with those watches. Often only handed over for special deep mission at the beginning. Good to know, that these watches started to see action in the late 70th. When the DRSD was developed long before that. Till then Comex mainly used 5513/5514 watches with valve. So i guess they took no chance for a product which did not proof it's quality for sure.