It’s a later design AP quantieme perpetuel which as likely know was the first production ultra thin automatic perpetual calendar which was monster success sold from 1978 for bones of two decades. Such a success that many saved AP from quartz crisis and vacheron & Patek would need to respond with their ref 43031 and 3940 in mid 80s. Base caliber the legend 2120 (jlc920) with perpetual module. The technical canvas as impressive as is only half the equation and was used as a canvas up express many a wild and unique design speaking to brazen individuality and commercialism of the 80s.
Looking at non-bracelet non-gemstone variants, AP roughly made 5 thousand watches of which vast majority cased in yg with a white dial but also home to other metals and wild rare dials and first skeleton perpetuels.
Below is my cheat sheet of refs/rarity
Here we have ref 25681pt - the first five of which were retailed and likely commissioned by William Asprey for Asprey Bond street; he had quiet the eye for design - even helping Roth go indie by commissioning batch of early tourbs sold under asprey name - I like to think of him looking for odd designs to compete with Cartier London next door.
Here pic of watch alongside an Asprey catalog of mid 90s
It is interesting to note that given amount of metal it is easily the heaviest non bracelet apqp being 20% heavier than a solid caseback platinum with say a Tuscan dial.
I could blabber on but those are main considerations of interest for me