HP-20S

The HP-20S is an algebraic programmable, member of Pioneer series of HP calculators produced from 1988 to 2003. It is similar to HP-21S. It has ninety-nine steps of fully-merged program and ten memory registers.

Libraries

There are six libraries in the ROM, which could be loaded to RAM and used and edited as user programs.

*A- [ROOT] finder, finds a root of f(x)=0
*B- [INT] integral, calculates definite integral using Simpson method
*C- [CPL] complex numbers manipulations
*D- [3 by 3] matrix manipulations and line equations solver
*E- [qUAD] quadratic equation solver
*F- [fit] curve fitting, using exponential, logarithmic and power functions

Design peculiarities

The HP-20S is not a clean design. It shares the quirks with its close relative, HP-21S. Some of them are:

*INPUT and SWAP keys, which are awkward and not clear solution to mimic RPN functionality.
*Absence of "x*A real bug is "x<=y" test. First of all, its name is misleading. Really, it is "x>=y" test in terms of RPN calculators. The manual says that "x" is 'hidden' while "y" is 'visible'. But "y"^"x" power key on the calculator's keyboards functions in the traditional fashion of other HP RPN calculators. The second problem here is due to algebraic design: in order to separate two arguments of a test you should divide them either with arithmetic operation or INPUT. If using arithmetic, like:

::RCL 6::+::RCL 7::x<=y?::GTO A

:you have "pend" announciator lighted, since calculator sees a pending addition operator. After the program stops, you can press "=" sign and get the result of pending operation. If you use INPUT instead of aritmetic operation, you'll see ":" anounciator. In order to hide this effect, you should place "C" clear command somewhere before program end.

Nevertheless, HP-20S is a functional and fast calculator, with very good LCD, keyboard, look, and feel. It uses the normal infix notation rather than RPN, which most HP scientific calculators use.

External links

*http://www.voidware.com/calcs/hp20s.htm
* [http://mycalcdb.free.fr/main.php?l=0&id=841 HP-20S] on [http://mycalcdb.free.fr MyCalcDB] (database about 70's and 80's pocket calculators)

Programming examples:

*http://www.hpmuseum.org/software/20stvm.htm Financial TVM calculations
*http://www.hpmuseum.org/software/20sbool.htm Boolean functions (AND,OR,XOR,NOT)
*http://www.rskey.org/detail.asp?manufacturer=Hewlett-Packard&model=HP-20S Gamma function