Hewlett Packard HP-21S

Serial number 3131S02836: 1991, 31st week, Singapore
Accessories Pouch

Manual: Stat/Math Calculator Owner's Manual (English), dated June 1990. 
It includes a detachable quick reference guide.
Condition Absolutely excellent!
Repairs, Comments -
Acquired 25.1.2003
HP codename, series Monte Carlo, Pioneer
Type, Precision, Input mode Scientific, 12 BCD digits, exponent ±499, Algebraic
Programmable Yes, keystrokes, symbolic labels 0-9, A-Z.
Performance Index
Memory 10 data registers (0-9), 99 program steps, permanent memory
Dispay 12 digit 7-segment LCD plus sign
Special features Probability functions, extended statistics, 6 built-in applications that can be loaded into program memory using the LOAD key: A: One sample test statistics, B: Two sample test statistics, C: Linear regression test statistics, D: Chi-square test statistic, E: Binominal probability distribution, F: Time value of money.
Original Pricing, Production 3.1.1989 ($49.95) - approx. 1992
Batteries 3x small button sized cells
Dimensions Length 14.7cm, Width 7.8cm, Height 1.5cm
Comment In principle a very powerful machine - but the lack of the RPN entry mode really makes things unintuitve. For example the big INPUT key: On RPN machines this would be the prominent ENTER key but here it doesn't have much functionality. It is only used to separate inputs for certain functions that require two arguments, like permutation and combinations. So you ask why addition or substraction would not be a function of two arguments? Well, right here the confusion begins! I tried "2 INPUT 3 +" but the result was not what I had hoped for.
The same applies to the other algebraic models: HP-10B, HP-18C, HP-19BII, HP-20S and HP-27S. The HP-30S is different in a sense that it was originally designed as an algebraic-entry model and didn't have to reuse the typical RPN style keyboard layout with the big ENTER key. The HP-17BII and HP-49G are different as well because they offer both RPN and algebraic mode.

Interestingly, the algebraic models were introduced only in the later 1980s with the HP-18C in 1986 being probably the first one. Also, half of these calculators are business/financial type models: The HP-10B, HP-18C, HP-19BII, and to some extent the HP-27S. A number of developments probably influenced this decision:

  1. Scientist were not using handheld calculators any more but rather the much more powerful PCs and laptops.
  2. Business people never liked (or understood?) RPN. 
  3. Handheld calculator sales declined in general due to more widespread use of PCs/laptops. To open a new market students and highschool kids had to be targeted with cheap and algebraic models (ie. HP-20S, HP-21S, HP-30S).
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