HP RPN's : deficiencies in stat summation Message #2 Posted by Karl Schneider on 25 June 2004, 1:07 a.m., in response to message #1 by bill platt
Hi, Bill 
Wow! That's dredging the archives. Yep, I wrote that, so here's the "short essay" I had in mind:
The usability of statisticalsummation functions on RPN HP calc's (not including the RPL HP28/48/49 and the algebraicbased 27S/17B/17BII) falls a bit short, in my estimation. This basic functionality was implemented more sensibly and thoughtfully even in older Casio and lowend TI calc's, as I see it.
On many HP RPN calculators:
1. Entering 2variable data pairs puts the values in reverse order.
This can be overcome on the RPN models by entering the values in reverse order, or with x<>y before SIGMA_+, but this is annoying. On algebraic models by HP and others, x INPUT y SIGMA_+ maintains the order of the data pair.
2. 2variable summation and calculation of standard deviation (SD) are automatically performed, even when unnecessary.
This sometimes causes problems, if "leftover" value(s) are used for ysummation in 1variable analysis, then SD is calculated. The "debris data" might cause a sqrt(neg) error when the SD function tries to calculate both x_SD and y_SD. Erroneous ysummation registers must be cleared before the x_SD answers can be obtained.
The 32S/32SII get around this by providing separate commands for x_SD and y_SD. The Casio and TI models typically have separate userselected modes for 1variable and 2variable analyses.
3. The ability to specify repeated data or datapairs is not provided.
By contrast, TI offers "FREQ" for entering repeated data. Casio calc's offer a similar capability.
4. Sample SD's, rather than population SD's, are calculated.
I never quite understood HP's emphasis on sample SD's. I would think that the most common applications for basic stat on a calculator would be a teacher computing mean and SD for class scores, or a student doing the same for laboratory observations. For either of these cases, the population SD would certainly be appropriate. It is no more difficult to obtain a sample SD by first subtracting the mean as a datum, as to obtain a population SD by first adding the mean.
Again, the 32S/32SII/33S offer both population and sample SD's. Menus made this choice easier to provide.
There are other gripes, many of which pertain only to certain models. For instance:
 The HP41 didn't even have 2variable stat built in (it could be added with a Stat Pac).
 The 34C/11C/15C omit certain useful functions (e.g., xestimate) and kluge others together as one function (yestimate and coefficient of regression). This situation probably stemmed from lack of sufficient available keyboard space.
Much of this is "water under the bridge", but I view this as one instance of something that HP didn't implement as well as its competitors.
 Karl S.
Edited: 25 June 2004, 1:14 a.m.
