How rare is this Carrera ?

Very rare. If you're searching for something like this, a 2447D (decimal) will be similar as its decimal track is also printed in blue.

1996
See: https://www.calibre11.com/heuer-carrera-1964-re-edition/

Um

If you want a brand new from the store watch, why were you originally asking about a watch from ~1966?

😝

P.S. the CS3110 suggestion from Mr. @elbeik was a good one; there are tons of them around for sale

Nobody knows for sure about vintage Heuer production numbers, but the sheer rarity of examples of the 2447P (and even rarer 3647P) suggests that far fewer were produced than the Decimal-scale model (which were often sold via Fisher, a scientific instruments company) and the Tachymetre-scale model. The internet only seems to know of a small handful of 2447Ps, and only one 3647P!

Heuer didn't seem to make a whole ton of Carreras in the 1960s, period - or at least, very very few are seen coming to market compared with Autavias. This may be due to the crazy spike in Autavia values bringing more of them to market, though when a Carrera comes up for sale nowadays, we see them going for crazy money. Some models are more easily found than others - 2nd-execution silver-dial 2447s, for instance, or 3647Ns - but others are absolute hen's teeth. In the time since I jumped on my first-execution silver text 2447N in late 2012, I have seen only one other like it for sale...

As to why the pulsation dial, I doubt Heuer had any special reason for it other than that the Carrera was a versatile line of chronoraphs, and adding a pulsations dial would have been a logical extension of the brand. After all, Omega had been selling the Speedmaster available with a pulsations scale on the bezel, so why not? Of course, only a few short years later, electronic timing equipment would have been adopted as the norm for most professional timing needs, especially in the medical profession.