: Thank you very much for your reply and thoughts on this Justin,
: very much appreciated.

: I had to do a bit of online research to learn what a Bayonet Heuer
: crown was and I think it's like an EPSA bayonet case back that
: uses a quarter turn to lock the crown. Is this correct?

: Is there any way--aside from removing the crown and stem--to tell
: if this was a screw down crown?

The crown tube on a bayonet crown will be smooth on the visible portion and the tube will be approx 2.2mm in diameter. The earlier screw down (unsigned) crown tubes will be larger on the visible portion at approx 3mm. I’ve seen hundreds of these watches and never seen a Heuer-signed screw down crown on a 980.006L. I’m pretty certain you have a bayonet crown.

The deep dive 1000m 980.023 (totally different case) came equipped with screw down Heuer crowns but those are the exception to the rule.