42S stat ops



I have a 42S (won it at an engineering frat rush party in '91!) I haven't used in ages and have long since lost the manual. It seems you can't find a manual online anymore, and can't buy it either. Sad.

Well, right now I simply want to use the MEAN and SDEV operations but have absolutely no clue as to how to use them. I have been tinkering with it for a couple days now and its not obvious to me. I have 3 numbers: how do I get them entered and get the mean of them? Ditto for stadnard deviation.

If some kind soul could answer me this I would be very happy. The rest I will have to figure out by playing with it.




entering the three numbers for statistics requires [Sigma +] (Sigma means the sigma symbol) to be pressed. Instead, you should have a look at the menu available at [÷] (division) key; just press [SHIFT][dvivision] and you are inside the Statistics menu.

Before starting, clear the previous menu data with [SHIFT][CLEAR] {CLSigma];

Then, one by one, enter each data (pair of data) and press [Sigma+], first key in the STAT menu;

After entering all data (your three numbers set), just press softkey for [MEAN] and [SDEV] in the same STAT menu.

If you need more info, send me an e-mail.

Hope it helps... for now.


Holy cow, it works!

I have an exam on Monday and this will make my life alot easier.

Thank you so much. Um... if I think of anything I'll email. :)


Good news! Hey, ar'u in Texas?

If'u need so, I'm here. Be my guest. Anytime.

Best regards.


MEAN acts as I would expect, but I see now that SDEV does something strange.

The Standard Deviation of 20, 25, and 45 should be 175, but the 42S tells me 13.2288! MEAN is correct (30), as is SUM (90).

Entering as such (after having CLSigma (cleared Sigma)):

STAT (menu)








(Yes, I will buy the CD with the manual, but it won't get here to save me for my exam on Monday.)


I think you've confused standard deviation and variance.

I recommend much studying before Monday. ;-)


Umm, right. I wanted SDEV^2, Variance.

Thank god for HP's products and the kind knowledgable folks on this forum. :)


SDEV^2 is close to the Variance, but its not the same thing (in this case you get 175.xxxx instead of a whole number: 175.)

Does the 42S do Variance? (What I should have asked from the start.)


Hi Xtian,

I can't answer directly because I don't have a 42S. However, I have performed the calculations on a 32SII. The result of squaring the sample standard deviation on this calculator is :


So I think it's just a matter of rounding error.

The more important issue is distinguishing between sample statistics, which use a denominator of (N - 1) based on loss of a degree of freedom, and the population statistics, which use a denominator of N. [N being the number of data points.] On the 32SII, the sample standard deviation is given by sx whereas the population standard deviation is given by
[lower case greek letter] sigmax.

If a calculator has only one or the other, then

sigmax2 =
[(N - 1) / N] * sx2


sx2 =
[N / (N - 1)] * sigmax2

Just take the square root to compute sigmax or sx.


Most HP calc's offer only the sample standard deviation "s". To obtain the population s.d. ("sigma"), the manuals generally advise entering the mean as an extra datum, then finding "s".

The 32Sii offers both "s" and "sigma".


You can get the HP42S manual from this site via the manual CD's.



You would want CD1, but the whole set is worth it.



Always remember to clear the summation registers before entering a new data set.

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