Seems to belong to the 73321 family, although the NS isn't listed on OTD: http://www.onthedash.com/watches/reference-73321/ Some info here on ref 73321S: https://hairspring.com/finds/value-proposition-nos-heuer-pre-carrera-73321s/ Found these on the NS as well, but not much historical info. http://chronoaddict.blogspot.com/2017/09/heuer-ref73321ns-poorman-carrera.html https://www.carousell.sg/p/heuer-classic-panda-chronograph-127527066/
I also see listings for 73323NS, 7823NS and 7821NS that all look like it might be it. So not really sure on the ref. number... http://chronoaddict.com/watches/show/id/206 https://vtgwtch.wordpress.com/portfolio/zodiac-7823-ns-2200/ (This article is the Zodiac re-branded Heuer 7823ns) http://chronoaddict.blogspot.com/2019/12/heuer-ref7721ns-poor-man-carrera.html