Juan --

So, if those stories you've heard are correct, that would explain why the one I bought more than a year ago was without manual, and that I've never seen a manual or calculator with manual offered on eBay.

The HP-21S is kind of a "niche" model that -- along with the HP-20S and HP-10B -- is a low-end Pioneer-series characterized by the 7-segment LCD readout. It does have some functions that are hard to find on other RPN or algebraic models.

A really *capable* Pioneer-series calculator for statistics would have utilized the high-end Pioneer hardware and firmware (i.e., HP-17B, HP-17BII, HP-27S):

- Equation editor with solver

- 7 kB RAM

- Statistics functionality that stores each datum

This would allow sorting, minimum, maximum, median, and mode. It would also prevent errors that occur from calculation of standard deviation from summation quantities, rather than from mean and deviations.

For example, calculate the sample standard deviation of

999,999

1,000,000

1,000,001

The correct answer is 1. However, on any RPN-based model or the HP-20S or HP-21S (which perform summations), an incorrect answer of 0 will be returned, due to roundoff error in the subtraction of summation quantities.

The HP-17B, HP-17BII, HP-27S and RPL-based models store the input data, calculate the mean and then the deviations. They give the correct answer.

The HP-21S, like the HP-20S, has those built-in keystroke programs (using LOAD) that are not intuitive to use, then wipe out program memory when they are loaded. Not the best of ideas.

The CD/DVD's available for purchase here at MoHPC include a PDF scan of the HP-21S manual.

-- KS

*Edited: 8 July 2006, 4:00 p.m. *