HP Forum Archive 21

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Roll-down key in HP-15C Message #1 Posted by Steve Ross on 14 Oct 2013, 2:11 p.m. The roll-down (and roll-up) key on my HP-15C do not behave as I expect them to behave. Would someone please explain the following behavior to me. Key X-register Comment ----- ---------- ---------- 0 0 Enter 0.00 Fill the stack with zeros. Enter 0.00 Enter 0.00 1 1 Rv 0.00 Roll-down 2 2 Rv 0.00 R^ 2.00 I expect to see "2.00". So far, so good. R^ 0.00 I expect to see "1.00", not "0.00"! Where did the "1.00" go? I see the same behavior if I exchange the locations of the two roll-ups and the two roll-downs in the above listing. Thanks in advance for your help, -- Steve Ross

Re: Roll-down key in HP-15C Message #2 Posted by Mark Hardman on 14 Oct 2013, 2:23 p.m., in response to message #1 by Steve Ross Think about it... 1 v 2 v ^ ^ - - - - - - 1 0 2 0 2 0 0 0 0 0 0 2 0 0 0 0 0 0 0 1 0 2 0 0

Re: Roll-down key in HP-15C Message #3 Posted by Richard Berler on 14 Oct 2013, 2:28 p.m., in response to message #1 by Steve Ross When you roll down after entering "1", the "1" goes to level "z", 4th stack level. When you enter "2", shouldn't this lift everything a stack level up meaning that you are now losing what was in level 4, your "1"?

Re: Roll-down key in HP-15C Message #4 Posted by Michael de Estrada on 14 Oct 2013, 2:34 p.m., in response to message #1 by Steve Ross As soon as you typed 2 in the x-register, the calculator did a stack lift and replicated the 0 in the z-register into the t-register, overwriting the 1 that had been there.

Re: Roll-down key in HP-15C Message #5 Posted by Marcus von Cube, Germany on 14 Oct 2013, 3:36 p.m., in response to message #1 by Steve Ross You can disable the stack lift that occurs when typing the 2 if you precede it with a Clx.

Re: Roll-down key in HP-15C Message #6 Posted by Steve Ross on 14 Oct 2013, 8:09 p.m., in response to message #5 by Marcus von Cube, Germany Thanks to all of Mark, Richard, Michael, and Marcus for your quick responses. I see that I didn't have a good understanding of "stack lift enabling" and that the stack lift did not actually "fire" until you key in the next digit. So I key in the first number, "Rv" enables the stack lifting behavior, and the second digit that I keyed in lifts the stack and causes the first number to be lost. Understood. Thanks also to Marcus for his "CLx" work-around. -- Steve

Re: Roll-down key in HP-15C Message #7 Posted by Nick_S on 15 Oct 2013, 4:12 a.m., in response to message #6 by Steve Ross You will find a web-based simulation of the HP-15c that has both the calculator interface and fields with the stack-levels and registers so you can see what is going on under the hood as you type in an example. http://hp15c.com/web/hp15c.html Nick Edited: 15 Oct 2013, 4:13 a.m.

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