FORTH & HP: where to start?

[Helix]

I you want a calculator, and accept non-HP calculators, you can try Forth500 for the SHARP PC-E500 (S), and Forth850 for the SHARP PC-G850 (V) (S) (VS).
They are based on the most recent standard of the language.

Forth500, that I know the best, is very complete. It can use two editors, TED and the built-in BASIC editor via TLOAD, and programs can be stored on a computer via a serial link, or with a cassette interface.