HP 12C Platinum Programming v. Gold Face

[Dean Lewis]

I have a program that calculates a Mortgage Equity Cap Rate Ellwood Method. It works fine on my Gold Face, but I recently purchased a HP 12C Platinum and the program gives an erroneous answer when I enter the same variables.
Can you assist? i.e. the correct answer produced on the gold face is 0.1154 while the answer on the Platinum is -0.4341
I have the program in PDF form that works on the gold face if I can email it to someone, please let me know.
dean.lewis@knoxcounty.org

Edited: 31 Oct 2013, 9:06 p.m.

[Kimberly Thompson]

Dean

I have both, happy to give it a go.

kimat@networksplus.net

SlideRule

[Andrew Feist]

Just as a general guideline, I would make sure your platinum is in RPN mode rather than ALG. (I suspect Kimberly's already got it covered, but if you need another pair of eyes you can click on my name for my email.)

[Kimberly Thompson]

Andrew

Are you familiar with any references to stack lift/enable/disable tables for the the 12 platinums?^{rhetorical question} (apparently at least three variants?)

I'm rewriting the program, relatively small listing, but the mechanics behind the problem might be of interest to a wider participation.

BEST!

SlideRule

[Andrew Feist]

I have no idea whether there's been any change in the 12c platinum behavior in this regard; I'm not nearly enough of a collector to have more than one of them, and mine certainly displays the "modern" stack-lift behavior. The current platinum manual doesn't have the financial keys on the list of keys that don't cause stack lift, while the "regular" 12c manual does.

If someone has an early platinum and can chip in as to whether their machine does stack lift, we'd like to know. (To test, just fill the stack with 0, do a TVM problem (say, 300 [n] .25 [i] 250 [PMT] [FV]), then roll through the stack. The "old" gold behavior is that you will have just the answer on the stack; the "new" platinum behavior is that the stack will also contain 300, .25, and 250.)

[Kimberly Thompson]

Andrew

Thanks for the reply. I modified the program in question to run on any variant of the HP-12 series. The question concerning stack behavior is a 'known' but as yet NOT fully documented behavior. Since the program enjoys copywrite, only the two modifed lines (above and below the modifications) are provided (see posting that follows). Thanks again & BEST!

SlideRule

[Kimberly Thompson]

Dean

The INITIAL offending line of code is PMT at step 08. The Y Z & T values on the 12P stack are different from the Y Z & T values on the 12C stack: only the X register values are the same, so when the next stack and register operations are performed, the two calculators are out of sync.

T = 1.000000, Z = 300.000000, Y = 1.000000 & X = -0.0105322 on the 12P

T = 0.000000, Z = 0.000000, Y = 1.000000 & X = -0.010532 on the 12C

This deviation continues til by line 25, only the X register values are the same, so when the next two stack and register operations are performed, the two calculators are way out of sync.

T = 1.000000, Z = 10.000000, Y = 15.000000 & X = -0.049252 on the 12P

T = 0.000000, Z = -0.126387, Y = 0.122436 & X = -0.049252 on the 12C

After this, little else matters. I'm looking at the respective manuals to try and understand this behavior, but this is a start. As I know more, I'll post here.

Members, any ideas for this behavior?

SlideRule

edited for clarity

Edited: 1 Nov 2013, 8:06 p.m.

[Andrew Feist]

The issue seems to be that the financial keys cause stack lift on the platinum, but don't on the gold. I think line 8 is ok, as PMT doesn't particularly care what's on the stack, but later it becomes important as the program assumes previously calculated values are still there.

You don't really need the program to see the different behavior; just fill the stack with 0, do a TVM problem, and then roll through the stack. I don't know why this behavior was changed, though.

[Kimberly Thompson]

Dean

The program works as advertised with the following two modifications;

   from

17       40  +

18    42 34  f CLEAR FIN

   to 

17       40  +

18    44  7  STO 7     inserted line

19    42 34  f CLEAR FIN

   and

25       14  PMT

26       20  X

   to

26       14  PMT

27    45  7  RCL 7     inserted line

28       20  X

Storage Register 7 is now used, like Register 0. This modification works on the 12c gold as well.

You have eMail for the complete NEW listing, enjoy!

BEST!

SlideRule

corrected typo 22>26 & folowing

Edited: 3 Nov 2013, 4:11 p.m. after one or more responses were posted

[Dean Lewis]

Kimberly & Andrew,
Thanks for your research on this problem. I had no idea it was such a technical issue. I have entered the changed program on my Gold Face and it works perfectly as the old. I will enter it into the Platinum this week.
Thanks again,

[Kimberly Thompson]

ALL

Quote:

---

message #6

The question concerning stack behavior is a 'known' but as yet NOT fully documented behavior.

---

A little further research on my part mutes my prior assessment. The table on page 175, Appendix A for the 12c gold enumerates the STACK following Financial Functions & the table on page 237, Appendix A for the 12c platinum enumerates the same. The STACK behavior is both known & documented.

In summary, the STACK lifts, FIN-X, x-Y, y-Z & z-T, following a FIN Function on the 12c platinum while the STACK overwrites, FIN-X, y-Y, z-Z & t-T, following a FIN Function on the 12c gold.

BEST!

SlideRule