HP 21S Manuals

I can only find very little documentation about the HP 21S Statistics Calculator here. It is even not taken care of on the Museum CDs. Well, I know, it's one without our favourite button. But, looking on the keyboard, it seems to cover the topic better than all other "simple" pocket size calculators I know (meaning I do not want to carry nor power up an HP 48SX for doing standard statistical tests - I've read the "leisure suit" discussion, I feel the same, still like good old RP*N* best).

Does anyone know where to get more info? Was an Owner's Manual shipped with this calculator at all? Where can I look into it?

Thanks in advance!



of course the unit was available complete with box and manual. AFAIK HP also produced quantities of the 21S as school class sets, with a number of bare units, and one manual for the pack.
So this could be the reason why there are so few 21S manuals floating around. The 21S is based on the 20S, with some statistical extensions. So for basic use, a 20S manual should do the job.
Another note: You know that the 21S in not an RPN calculator...




I once had a 20s (long story) now i'm an RP*L* fan thanx to my 28s, but anyway... if i can remember, the thing with the 20s was that the built in equasions would put results in some of the 10 memory registers. On the 21s, you'd need to know which registers contained the variables and results of the various built in equasions, so you can't really use the 20s manual unless some of the library is the same.

The 20s/21s is really easy to use though, I'd like to have a 21s myself. I'd reeeeealy like a 42s+ with a 2 line display, but that's another show.



The 21S seems to be one of very few programmable calcs that provide means to calculate the inverse of some frequently used probablity distributions (t, f, chi-square, normal). The 28S does this and probably its successors. However, I find programming in RPL cumbersome. Recommendations are welcome.

Programming the inverse t-distribution on other calcs doesn't seem to be a trivial task. It's possible to use Abramovitz' approximation but this would require a solver to solve for x given an integral. I'm still trying to implement it on my 42S.

Consider yourself lucky to find one of these rare units. Unfortunately, I don't know where to acquire a manual.


I would use numerical solve to find the inverse...


Thanks to everyone. Nevertheless, I still do not know a source for such a manual. Wouldn't that be something for this museum? Just for sake of completeness ;) Who knows a friendly guy having access to it and willing to scan it in?

VPN, could you explain to me how to do this? I have a 32s and a 42s, so SOLVE is available.

RDT, I know the hp21s comes without RPN, but nevertheless it is the calculator providing useful statistical keys I can't find anywhere else. Of course I would welcome it having RPN, too, but ... at least it has the neat appearance of a true HP.



Click Lower Right Corner "Support & Drivers"


"See support and troubleshooting information"

for: HP 32SII [ENTER]


Click the last item "product information"


Click the only item "manuals"


From here on I suppose you know how to right-clik and select "Save Target As..." to download the PDF



Thx, VPN, for the perfect description. I fetched the HP32sii manual. HP21s is (of course) supported by HP no more. So I keep on searching.

But, what I wanted to ask you in my last message was how to use SOLVE in getting the inverse normal distribution. I found something about this topic in the HP32sii manual, but not taking SOLVE. Just for curiosity, because you proposed to use it. Sorry for posting my question in a misunderstandable way.


The idea is to look for a formula that gives an approximation to the normal distribution function and prgramming it for use with the solver. Then it'd be possible to solve for x given an integral.

It's also possible to program the function itself (not difficult), and use numerical integration and solve in the program. But that's probably much too slow for 3 digits of precision.

Numerical recipes for all kind of problem can be found in Abramovitz and Stegun, Handbook of mathematical functions, which is available on the web IIRC.


Of course an off the shelf Hp21s came with the manual. However, not many people purchased the Hp21s as it was about twice the cost of an Hp20s and for the money, you could buy an Hp22s which WAS better. The Hp22s had a solver, the Hp20s and Hp21s did not. They are programmable, but no solver. Therefore, finding an Hp21s manual will be difficult. However, it does program exactly like the Hp20s but with three different built in libraries and the stats features (which I believe are pretty straight foward, and located under the numerics).

I do hope you can find a manual, I bought my 21s as a surplus service replacement and did not recieve a manual either. My wife contemplated using it in a stats class (and we both explored its many features), but she was much better served by her 27s (no graphics calc's were allowed).


The HP 32SII Manual has in Chapter 16. Statistics Programs (16-11, PDF page 275) an example of Normal and Inverse-Normal Distribution.


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