Might was well wax nostalgic too!

When I went to college (80s) I got an HP-11C first, then HP-15C and then HP-16C. Handy. The 11C went to my sister when she entered college and I upgraded to the 15C. Lost my HP-16C out on a job somewhere after college (man I missed it), so a few years ago I found another and acquired it as 'New In Box'. Cool! Still use them once in awhile. Also picked up a HP-12C for around the house calculator. Those financial calculators are still made (not quite the same key quality unfortunately ). Took to RPN like a duck takes to water. RPN works so well, can't do without it . No need for a graphing calculator. I also found an HP sim (42S?) that I use on the Linux workstations too. Keep it up on my desktop all the time. That works too as long as you are 'seated' though .

Swissmicros looks like they still make some clones of the HP calculator.

Hewlett-Packard's HP-3000 minicomputers also used RPN ... Don't remember about the HP-2000 or 1000 anymore, except I do know that the 2000 had field-programmable microcode.

Hewlett-Packard's HP-3000 minicomputers ... could RPN be anterior to that ? PDP ?

The DEC computers (PDP, VAX, etc.) did not to my knowledge use RPN internally.

I still have my HP-16C and to this day I still use it. Virtually indestructible and well thought out.