I spotted this on ebay, and something made me look a little closer.
First impression is that it is a reprinted dial, and there is nothing else like it that Heuer made, so dismiss it..

Then I looked a little closer.. and guessed that underneath the hands and dial is a Carrera trying to get out. The box has both 3647 & 7753 N printed on it, although that is a loose connection.

I also guessed that other savvy Heueristas may have spotted the potential, as bids went above and beyond what you'd expect for a stopwatch, especially one that didn't seem right.

So.. hopefully someone here bought it, and if you did, please let us know if it is indeed the 'ultimate sleeper' with a nice Carrera 'under the hood', ready to be restored to it's former glory with a correct dial and handset.

The watch, with loads of big photos...
http://www.ebay.co.uk/itm/Vintage-Tag-Heuer-Stopwatch-Timer-Chronograph-Unusual-Wrist-Worn-/121180428552?_trksid=p2047675.l2557&ssPageName=STRK%3AMEWAX%3AIT&nma=true&si=0otE%252FSSz3Gjm0CmWa61Cmp%252BNut0%253D&orig_cvip=true&rt=nc

Stewart
- Heuerville