42s and 15c


I've seen several statements in this forum and in other places that the 42s and the 15c are very different calcs. I realize that the layout and display is different, but as far as functionality are they really that different? They both do complex numbers, matrices, and programming, right? I still use my 42s on a daily basis but is it worth investing the $150+ to find out?


The HP-15C does complex numbers, and it does real matrices, but it does not do complex matrices. You can use "tricks" to simulate some operations on complex matrices. See the "HP-15C Advanced Functions Handbook" (available on the Museum CD-ROM) for the details.


Eric posted,


The HP-15C does complex numbers, and it does real matrices, but it does not do complex matrices. You can use "tricks" to simulate some operations on complex matrices. See the "HP-15C Advanced Functions Handbook" (available on the Museum CD-ROM) for the details.

Rarely do I have the inclination to differ with Eric Smith's excellent posts, but here's a minor exception...

It's true that the 15C stores only real-valued variables as matrix elements, which requires the user to represent complex-valued matrices as real ones with twice the number of elements. However, the user may perform many of the same matrix calculations for complex-valued matrices, by executing mathematical transformations that are done internally by software that handles complex-valued matrices.

The designers of the 15C supported complex-valued matrix operations by providing these necessary transformation utilities (not "tricks") as built-in keyboard functions.

The utilities are reasonably intuitive for anyone who is sound in linear algebra; are easy to use; and are documented in the excellent, standard Owner's Handbook as well as in the optional, extra-cost Advanced Functions Handbook.

IMO, the built-in utilities for using complex-valued matrices is an excellent example of how HP "went the extra mile" to develop a fully-engineered and functionally-coherent tool for professionals. In that regard, the successor 32S/32Sii and 33S, despite their advantages, don't quite measure up.

-- Karl S.


The 15c has a very small memory compared to the 42s. THe latter is large enough to take any 41CX program (a 41 withyout Zenrom or other super-whizbang aftermarket add-ons).

The 15c is a beautiful thing, period. But if you are used to the 42s, I think you will find the 15c a step backwards in time.

Every command is on a key. There is no alpha mode. That is part of the beauty.

Since I don't have a 42s, I dont't have that problem! :-)




Ah bill.....
I read your insightful posts often. Never would have guessed you don't have a 42s. I like the 15C as a handy, sturdy calculator but when I want to get serious I even skip the 48 and go for my 42s...sorry, one of my two 42s (never saw the need to use them both at the same time ;-)


Hi Dano!

Thanks for your nice note. Well, I would love to have a 42s--but it is hard to get one at a small price! I did miss one for $102 about a week ago, though. Someday.....

Best regards,




I see others have already found their words to express what is between both HP15C and HP42S. I guess that we can all add one or another extra information, because they are so many. I think I can post about a lot of them: plenty of memory "space (standard 8KBytes, upgradable to 32Kbytes or 64KBytes) IR output, control and system flags, enhanced programming with ALPHA labels instead of keycodes, menu-driven (I like it very much, although some users hate it), variables AND numbered registers, enhanced statistics with standard four curve fit plus BEST (auto setting for best correlation coefficient), full dot-matrix LCD with graphics capabilities (I never understood why some guys mentioned the HP42S is not a graphic calculator... if graphics can be drawn in the display, why isn't it graphics?). About math capabilities, Eric Smith mentions a very important difference between them both: the complex matrices. The fact is that when the HP42S is dealing with complex matrices, it uses half the number of registers needed in the HP15C to accommodate the same data in order to perform some complex matrix operations. Yes, the HP15C arrangement is clever, thoughtful, a true brainy accomplishment. I'd be proud of working with the team that developed the HP15C firmware. Ï remember that once I measured how much each matrix uses of the HP42S available memory and, as expected, matrices have a different scheme of memory usage. I took some (hand written) notes but I cannot imagine where are they (time to start again or look for this information somewhere), so I cannot see a way to compare memory usage in this case.

I just would like to add that I own each of both, and I like very much using each of them. Heavy duty work with the HP42S (faster and with more memory), but for daily enhanced tasks, I see no other better and easier as the HP15C.

Wow! Too much words, not so much additional information. But I hope these posts actually help you finding your own answer.


Luiz (Brazil)

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