Value of HP28C vs 28S?

[Dave Dirckx]

I have very nice memories of my HP-28C. I remember solving a linear system of 10 unknowns as the only one (with exact results) during an exam where we were allowed to use any calculator.

I never had the impression that I was fooled by HP when the 28-S came out. I was used to be careful with the memory storage, and for me and some students, it was a calculator with capabilities that were unseen in any other calculator. It was the first RPL, it should be worth something.