I want to acknowledge Max Stone's excellent article entitled "HP-80 History, Design and Interesting Facts" which is now in the Articles Forum of the HP Museum.
It's wonderful to have this as not much has been written about the HP-80. While the HP-35 was the first scientific pocket calculator, the HP-80, introduced a year later was the first financial calculator of any size (that I know of) and probably the first calculator to have any type of solver (in this case for the time value of money calculations). It must have sold extremely well as HP kept it on the market for a full 5 years even as the HP-70, HP-22 and HP-27 financial calculators were sold, and I gather that quite a few are still running 40 years later.
My thanks to Max for this excellent article!
Bob