Darren,
Yes, it's another Heuer oddity I'm afraid. It was almost as if Heuer hadn't sorted out the correct format for the divers.
IIRC, there are very early quartz versions of the Monnin, which have 844 type model numbers. (Maybe '8444' or something like that).

The quartz orange diver is 980.007, the auto 980.005. The orange diver was conceived early on - seen alongside the Monnin with cathedral hands in the '79 catalogue.

Stewart

: Outsanding watch & photo's.
: I read & enjoyed your review of the watch on your blog site
: Stewart and was a little surprised to see this designated as a
: 980.005.
: I had assumed that the auto version of this watch ( be it black or
: orange model ) would have been an 844 series watch. Further to
: that i thought the 980. prefix always indicated the watch was
: battery powered.
: Clearly i assumed incorrectly but where exactly do the model
: numbers cross over from 844 designation ?
: I have seen the 844 used all the way up to black dialed 844/5 under
: the ownership of Tag Heuer.

: Cheers - Darren