HP-41 and 42s: AIP with or without sign?

[rprosperi]

Well, at least if they have to be different, making it 'better' or more accurate, is a good reason.

No doubt there were complaints about the Advantage implementation (which was documented correctly, so 1 point for that); if someone wanted to preserve the sign it's a pain to check absolute value and prepend the "-" sign while preserving the stack values prior to AIP, while on the 42S a simple ABS would remove it.