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I write from rome italy and just now i recevived an calculatro hp 28 s

do you thing is son nice for collection?
tomorrow i'll buy the batteries
(i hope to find)

Hi Claudio,
a quick reply from Milano: a 28S is as good for a start as any other HP calculator built before 1999.
As far as batteries are concerned you should be able to find them (N size); try in a photo shop if anything else fails.


Claudio --

I certainly believe that a 28C or 28S (either one) is worth collecting, if not necessarily to use as one's primary HP calculator.

I find the 28 to be the easiest-to-use RPL model, with its uncluttered keyboard, dedicated alpha keypad, and "cheat sheet" on the left half. It also offers a nice units library with SI dimensions of a wide variety of metric and English units of measurement.

The 28S is an improved version of the 28C, with more RAM (32 kB vs. 2 kB), a faster processor, directories, and a few more mathematical functions (e.g., PERM, COMB).

The 28 takes 3 "N" cells. This is unfortunate, as these are typically sold in packs of 2. Be careful not to damage the battery cover, which is poorly designed.

-- Karl S.

Edited: 19 July 2004, 12:21 a.m.

I concur to that! The 28C and S are excellent machines, their only flaw being the battery door. The folding mechanism never failed for me. If you do a lot of programming, the S model is definitely in order, as the C is really under-powered in that respect. Otherwise these are fine machines, and being less endored by the hp community, they aren't too expensive on ebay.


I have currently a tuff situation:
HP 28S vs HP 15C
Which one is better - apple or orange?
Could you ever compare these quite different calcs?
which HP you would call a lemon?

Best regards from V.

Please what?


the newer 19BII units have a much better battery door construction. Cheap but simply better;-)

Too bad they didn't use that mechanism in the 28S...


I would say the HP 12C Platinum is the lemon.

"Which one is better - apple or orange?"

Apple! I like Mac's. I don't know that other manufacturer... :D


  1. The HP28S is fully alphanumeric. The HP-15C is not.

  2. The HP28S uses advanced, high-level RPL. The HP-15C is low-level RPN, keystroke-programmable.

  3. The HP28S has a multiline dot-matrix display. The HP-15C has just a one-line, segmented, non-alphanumeric LCD

  4. The HP28S has a multitude of advanced objects, fully nestable. The HP-15C only deals with single numbers and 2-dimensional, small real matrices.

  5. The HP28S has 12-digit accuracy with exponents up to +-499. The HP-15 has 10-digit accuracy, exponents up to +-99

  6. The HP28S has a full menu structure, including a help facility for commands and functions. The HP-15 does not.

  7. The HP28S can communicate with an external printer via I/R. The HP-15C has no communications whatsoever.

  8. The HP28S has 32 Kb RAM. The HP-15C has less than 0.5 Kb RAM.

  9. The HP28S does admit named variables. The HP-15C is limited to numeric registers.

  10. The HP28S does symbolic computations, including arithmetic, Taylor series expansion, polynomial integration, and equation solving including isolating variables. The HP-15C does not.

  11. The HP28S is very fast, much faster than a 41C. The HP-15C is slower than a 41C.

  12. The HP28S does include SYSEVAL for direct access to internal routines. The HP-15C has no such equivalent capability.

  13. The HP28S has an 'infinite' stack capability, including advanced UNDO features. The HP-15C has just 4-level classical RPN stack with LASTx as the only undo capability.

  14. The HP28S can evaluate algebraic expressions. The HP-15C can not.

  15. The HP28S has an elegant clamshell design that fully protects keyboards and screen. The HP-15C has no such protection, its logo tends to fall apart or get damaged, and its display tends to gather dust within.

  16. The HP28S has an internal timer which can be accessed and utilized in user programs. The HP-15C does not.

  17. The HP28S can do graphics, including reasonable resolution plots. The HP-15 cannot.

  18. The HP28S has user-adjustable display contrast. The HP-15C doesn't.

  19. The HP28S has a very extensive set of functions which covers just about everything you might wish or need. The HP-15C has a much more limited instruction set.

  20. There's also very extensive documentation on the HP28S internals, including several books by its very 'alma mater', Mr. Wickes himself. Next to nothing is known about HP-15C internals, nor does it exist any such documentation or reference apart from a few not too detailed articles.

Yet I would gladly give you two or more HP28S for a single HP-15C in mint condition, and would not part with my own HP-15Cs for any amount of HP28S's you could offer.

Best regards from V.

21. Complex Numbers:.....
<will be filled with an explanation by VA>

I don't understand what you want, VPN.

Seems to me you've been an HP fan long enough to know about all the many differences between the HP28S and HP-15C some of which I did mention, and that you also fully well know that asking "Which one is better" is plain downright silly, so I'm at a loss at what you exactly want or what point do you want to make, i.e.:

  • Just start some long and pointless thread about who prefers which ?

  • Just get to know about some fine-print differences you want specially discussed or commented ?

  • Just to make you feel better because you've located an HP28S you can afford, but no affordable HP-15C's on sight and you want to play Aesop's fable for a while ?

  • Just to reinforce the warm feeling that who needs an HP-15C when it's obvious an HP28S is much better ?

Please state some rationale why you want people to give their opinions on this (IMHO) 'silly' question of yours, and perhaps I'll consider giving my opinion, if that's what you want. But, honestly, your question seems to me as silly as they get.

And if you're serious and it's not some way to have some fun, well ... you seem to be a little 'unfocused'.

Best regards from V.

I don't think I can expand any upon Valentin's 20 point comparision, because these two are just that, An apple and an Orange.

The Hp28s evolved into the present Hp48/49 series with big improvements in both hardware and software. Yes the keyboards and build quality of the new 49 may not be as good as an older 28s, but their battery doors don't fail.

The Hp15c kinda evolved into the modern Hp33s. I say kinda, because unlike the Hp 28s which improved through evolution, the Hp33s is not real step up in all the most important aspects of the Hp15c (size, matrix support, quality). Nothing added but RAM, with no real support to ues that RAM.

And I would trade a couple of 28's for a single 15c any day, also.

And now for my typical RANT!!! But I just might take a 28s over a 33s, especially to an NCEES exam, if it were allowed, because the 28s can use its 32K of RAM. But that isn't the case so I will probably buy a 33s (though I am CHEAP and might just use an Hp32sii / Hp15c combination). And I am paticular, if the calculator misses a single keystroke, I get somewhat irritated. Make a $50 RPN calculator that isn't comparable to $10 cheapies in keyboard quality, and I get very mad. That is another of my gripes with the new Hp's.

My new replacement Hp49G+ has also failed me on rare occasions. If I used it more often like my older Hp's, I suspect it would fail me on even more numerous occasions.

I recently got a 33S for an NCEES PE exam. So far I am reasonably satisfied with it; it appears to be the best available choice for NCEES exam purposes. And I have not had any problems with the keyboard.

The 33S is certainly not flawless. The chevron keyboard is silly, the decimal point and the ENTER key are too small, the display contrast is not great, and the lack of variables and labels hinders programming.

But it has some important advantages as well:

(1) NCEES approval. NCEES has now explicitly banned the 39, 41, 48, and 49 series, as well as the 42S. The 28 series has not been explicitly banned, but it appears to be illegal based on its alphabetic keyboard and IR port. Even
old standbys like the 11C and 15C may be prohibited in the future; NCEES is seriously considering a ban on all calculators except for those with explicit NCEES approval. As of now, the only RPN calculators with such approval are the 32S, 32SII, and 33S.

(2) Large memory for equations. The 33S can't store too many separate programs, because it has relatively few labels and variables. But it can store a whole lot of complex equations, and for NCEES exam purposes, this is useful. For comparison, the time value of money equation alone eats up about 25% of the available memory on a 32SII.

The 33S is arguably the premier NCEES exam calculator on the market today; even algebraic users are buying it over TI or Casio models. HP ought to get some credit for introducing a model that successfully targets this market niche, although admittedly it is a relatively small one. Maybe they just got lucky.

Norris posted,


Even old standbys like the 11C and 15C may be prohibited in the future; NCEES is seriously considering a ban on all calculators except for those with explicit NCEES approval. As of now, the only RPN calculators with such approval are the 32S, 32SII, and 33S.

Not if I can help influence that decision. I have already written several communiques to NCEES via mailed letter and e-mail, advocating inclusion of the 11C, 15C, and 20S on their "Approved" list. I will follow up again before their August meeting.

(Yes, folks, I know that many other HP's also meet the standards; however, NCEES wants to keep the list short, and these models are the best and most commonly-available compliant models.)

Edited: 22 July 2004, 2:23 a.m.

Hi Valentin, guys; are you well?

I'm just taking the opportunity to ask a question (again, if I remember it well, but I am not sure you read it at that time) that I am not able to answer myself(not enough knowledge). I am hoping that you are able to give some reasoning to this question, and it involves matrices, complex numbers and the HP15C.

If this is a known subject with a known conclusion, please forgive me not being updated... 8^( Well, here it goes:
It's well known that the HP15C designers (Dr. Kahan amongst others) used clever software "maneuvers" to handle "real-number" matrices and achieve complex-equivalent results for inversions and system solving. Although what I ask is not mainly important given what can be done with the HP15C, I tried to find a way to calculate the complex number equivalent to the determinant of a real-number coded à matrix and did not succeed. The determinant for the real-number coded à matrix is a real number equivalent to the square of the determinant of the original complex matrix A. Or, in other words, the square root of the determinant of the real-number coded à matrix is the magnitude of the determinant of the original complex matrix A. All other HP calculators with embedded complex capabilities deal with complex matrices and calculate the determinant as a complex number. BTW, all of them followed the HP15C footsteps... anything else to say about this amazing little giant?

Do you know a way to calculate the real and imaginary parts of the determinant of a real-number coded, complex matrix in the HP15C?

Again, if this is a well known problem with a well known solution, just let me know and I'll "shame on me" and find my way home...


Luiz (Brazil)

123456 to remove

Edited: 21 July 2004, 1:10 a.m.

Yes - this kind of information I was hoping for.
I can't ask about it, because I don't know in advance what to ask - what others have bumbed into...

The Hp15c kinda evolved into the modern Hp33s. I say kinda, because unlike the Hp 28s which improved through evolution, the Hp33s is not real step up in all the most important aspects of the Hp15c (size, matrix support, quality). Nothing added but RAM, with no real support to ues that RAM.
Would it not be more accurate to say that the 15C kind of evolved into the 42S, and then became extinct? The 11C kind of evolved into the 32S, then 32Sii and now the modern 33S.

Concerning the NCEES:

The 28s became banned the moment Text entry of the graphics came into question. It was banned in many states even before the graphics calculator ban (not all states, but many, because of its alpha numeric keyboard, even though it wasn't QWERTY).

A couple of calculators that are still better than the 33s and would probably sneak past the proctors (at least until the NCEES sees these on their RADAR screen) are the Hp27s or even the Hp17B series. Both have the same hardware as the 42s and therefore, technically are banned. But they are not explicitly banned and looking at either, most proctors would assume just a simple scientific or in the case of the 17B, "What is that idiot bringing a business calc to an Engineering exam?".

Granted, if you brought the 17B you would also need a good scientific, but with its solver and long variable names, you would be able to load up some pretty good formulas that have a high probability of being on the exam.

I briefly considered the Hp27s, but I feel that I should either pass with NCEES restrictions or I don't deserve to pass. Therefore, I will either buy a 33s or just use a 32sii.

I still miss the features of a 48G type calculator, but part of engineering is also working within constraints.

Hi Jeff,

Or, you could say that the 41c mated with the 15c and produced the 42s, which became extinct. The strongest 41c genes were lost (I/O, synthetic/ML) and replaced by the weakest 15c genes (no I/O).



My recommendation: do not attempt to sneak an illegal calculator past the proctors and into an NCEES exam.

It's probably true that the average exam proctor knows little or nothing about calculators -- but there just might be a state board employee with actual engineering experience at the exam site, with the ability to recognize an IR port. The proctors can and do pick up unusual calculators for close scrutiny during the exam; after all, there's probably not much else for them to do during those 8 hours.

In California, you now have to sign a form in the exam room immediately before the exam starts. You must attest, under penalty of perjury, that your calculator complies with NCEES rules (for NCEES exams) or California rules (for state-specific exams).

Enforcement varies, but at least some state boards take the calculator restrictions very seriously. Stick with the 33S, 32SII, or some other NCEES-compliant model.

Jeff posted,


"Would it not be more accurate to say that the 15C kind of evolved into the 42S, and then became extinct? The 11C kind of evolved into the 32S, then 32Sii and now the modern 33S.

I would say that that the 42S was produced an improved, extended implementation of the "calculator only" portion of the 41CV/CX, building upon integrated capabilities pioneered in the 15C. The 42S is the only calc whose programming paradigm is the same as that of the 41; in fact, there's even a section in the 42 manual about compatibility with programs for the 41.

The 32S, by contrast, was developed to replace both the 15C and 11C. It offered new capabilities while omitting several important ones from the 15C, presumably to separate it from the upscale 42S.

The incompatible "replacement" for the 41 was the 48SX, introduced the same year as the 41 was discontinued.

Personally, I think the 48S/SX ought to have been a "super 42S" with RPN (adjustable stack?) and 27S-style equation "solver/evaluator/plotter", rendering the 28S and its unique RPL, like Prohibition, an unsuccessful "Noble Experiment".

Edited: 22 July 2004, 2:27 a.m.