An enhancement to classic RPN used by HP's graphing calculators and the C47/R47
Over time, the notion emerged that values being keyed in belong in an input buffer separate from the stack, and only copied to the stack when entry was finished, either by pressing ENTER or a function or operator which then "closes" the entry "mode".
This behavior has been called Entry RPN, or eRPN for short, and is different from classical RPN, where the transition of values onto the stack follows slightly more elaborate rules. See HP RPN Evolves for more details.
The difference in behaviour produces different results:
Entry RPN: 47 ENTER × results in 0
Classical RPN: 47 ENTER × results in 2209
eRPN/RPN is selectable in the C47 MODE menu.
