The Museum of HP Calculators

HP Forum Archive 13

 RPN - why 4 registers?Message #1 Posted by adam on 2 Nov 2003, 12:11 p.m. RPN newbie here. Since the Z register is already available for a constant, why do I also need the T register? How do I use the 4th level in the stack?

 Re: RPN - why 4 registers?Message #2 Posted by bill platt on 2 Nov 2003, 1:12 p.m.,in response to message #1 by adam With only 3 levels (the earliest machines--pre-handheld) you really do not have enough levels to deal with pending operations without being very careful. 4 levels seems just about right for almost all the time--any more levels hand you cannot relly remember how many pending ops you have going! Regarding the constant--the Z register does not make a constant---the T does---T duplicates itself any time the stack drops a level (after an arithmatic operation between x and y for instance). So, fo a constant, you "load the stacK" thus C puts the C in all 4 levels. now, any new value typed into X may be operated against the Constant. To operate a new item against the constant, simply type backspace or clx, to clear the last result, and type the new number to be operated on, and then operate on it. (Don't hit "swap" after clearing though, as that will enable the stack and you will have a "0" in y!) Alternatively, you can use the LST x register to hold a constant--but then you have to do a "swap" (also called x>

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