HP-25 statistics weirdness
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10-09-2023, 12:27 PM
Post: #1
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HP-25 statistics weirdness
Ever notice the HP-25 does not accumulate the y^2 value in a stat register? Makes things like computing r^2 for linear regression a chore as you have to account for it in your code on data entry. Also, RCL Sigma+ is not allowed - making our fearless pilot Mr. Sweeny hit a couple of extra keys - not to mention having to remember where SigmaX and SigmaY are stored.
Doing a little research, I found the HP-25 is unique in this. It's predecessor, the HP-55 has both y^2 and RCL Sigma+, and so does it's successors, the HP29C and the HP-33E/C. The HP-27 has y^2 but lacks RCL Sigma+. I presume all this weirdness is due to space imitations? And yet the 25 has percentage and NOP ? -J |
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10-09-2023, 08:37 PM
Post: #2
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RE: HP-25 statistics weirdness
I could imagine that \(\sum y\) and \(\sum xy\) can still be useful in case of a frequency table.
You can interpret \(y\) as frequency and \(x\) as value. The mean is then: \( \bar{x} = \frac{\sum xy}{\sum y} \) Example: \( \begin{array}{|c|c|} \hline Frequency & Value \\ \hline 3 & 7 \\ 5 & 11 \\ 2 & 13 \\ \hline \end{array} \) CLEAR REG 3 ENTER 7 \(\Sigma +\) 5 ENTER 11 \(\Sigma +\) 2 ENTER 13 \(\Sigma +\) RCL 5 RCL 4 \(\div\) 10.20 |
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10-09-2023, 09:31 PM
Post: #3
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RE: HP-25 statistics weirdness
BTW,
How did you get the sigma symbols to display in your post? I looked and could not find that in the editor. -J |
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10-09-2023, 11:50 PM
(This post was last modified: 10-09-2023 11:55 PM by Thomas Klemm.)
Post: #4
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RE: HP-25 statistics weirdness
You can hit the
![]() In this case it is embedded LaTeX, or specifically \sum for the \(\sum\) sign. Or then \Sigma + for \(\Sigma +\). |
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10-10-2023, 01:18 AM
Post: #5
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RE: HP-25 statistics weirdness
(10-09-2023 12:27 PM)John Garza (3665) Wrote: Ever notice the HP-25 does not accumulate the y^2 value in a stat register? Makes things like computing r^2 for linear regression a chore as you have to account for it in your code on data entry. Also, RCL Sigma+ is not allowed - making our fearless pilot Mr. Sweeny hit a couple of extra keys - not to mention having to remember where SigmaX and SigmaY are stored. I believe you are correct about why that feature was not included. As William C Wickes has said on other HP calculator projects when asked why a feature was missing from a particular model, "Life is short and ROM is full". In the case of the HP-25, this is literally true. There was no room left in the HP-25's ROM to add *any* feature unless you removed a feature or were able to further optimize the code to make more room. https://www.hpmuseum.org/forum/thread-85...l#pid74865 I suspect they put a higher priority on the percentage and NOP functions than on accumulating the y^2 value in a statistics register. Considering the HP-25 didn't start out as a programmable calculator, I think they did an amazing job including the features they did in the very limited ROM space they had available. |
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