I honestly begin to despair of watchmaker's pronouncements on some of these things, although I understand it is difficult when they have to be a generalist on the tens of thousands of watch models out there...

All the early Carreras used Valjoux movements (the 72, 92 and 723/72c) with one exception, that being the Landeron 189 in the 45 Datos. The first Lemania movement to find its way into a Carrera was the 5100 used in the 510.511 and 510.523 from around 1984. Lemania movements were again used in the first Carrera re-issues by TAG-Heuer, until Swatch squeezed the supply of Lemania movements to non-Swatch group brands.

Secondly, all these early Carreras had the Carrera name on the dial (above the Heuer shield), again with one exception, that being this time the 12 Dato triple calendar watches.

Thirdly, that's not a Carrera case. The angle and detail of the lugs is wrong for the Carrera case, but it does look like the economy models that were sold alongside the Carrerras at the end of the 60s/start of the 70s. Check the two watches at top left in the picture below for similarities:

That ties in with the Tachy scale on your watch, as Heuer had been using a different style until this point.

If you look closely, you'll also see those watches have a distinctive internal bezel, used for measuring fifths of a second. It's missing from your watch but that polished ring around the dial makes me think it was once there but has been removed at service - the markings on the bezel can fade or break, and I have seen a few watches where it has been removed for aesthetic reasons. For me, even a faded internal bezel looks better than none, so that's something you might look into getting back onto the watch if it's important to you.

So we have what looks like one of the 73321 watches of circa 69-71.

Except we still have a couple of mysteries here. Firstly, I am only aware of the economy watches being made in two-dial versions rather than your three-dial watch. That would make it rare in itself. But you can help us out here - by this time, Heuer had adopted a practice of engraving the serial number between the top lugs and a model reference number between the bottom lugs (earlier watches just had a serial # between the bottom lugs). If you can tell us these numbers (you may need magnification to read them and they are sometimes removed by cases having been polished), it will help with both dating and in identifying the model in question.

Secondly, there's that Lemania movement. A movement photograph would be brilliant to help us identify exactly what movement we're talking about. I am aware of 3 possible three-register Lemania movements it could be, but a photo would help settle that. And a request to the other OTDers - does anyone have a 73321 to be able to check what movement it uses?

If we can get the above information, I believe we can get to the bottom of exactly what you have there and better be able to give you an idea of its value - and I do like to have a mystery or two to investigate!