The HP-20S is an algebraic programmable, member of Pioneer series of HP calculators

HP calculators

HP calculators are various calculators manufactured by the Hewlett-Packard company over the years.- History :In the 1960s, Hewlett-Packard was becoming a diversified electronics company with product lines in electronic test equipment, scientific instrumentation, and medical electronics, and was...

 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
  Reverse Polish notation
  Reverse Polish notation is a mathematical notation wherein every operator follows all of its operands, in contrast to Polish notation, which puts the operator in the prefix position. It is also known as Postfix notation and is parenthesis-free as long as operator arities are fixed...
  
   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 should the user divide them either with arithmetic operation or INPUT. If using arithmetic, like:

RCL 6

+

RCL 7

x<=y?

GTO A

the display has "pend" announciator lighted, since calculator sees a pending addition operator. After the program stops, the user can press "=" sign and get the result of pending operation. If the user uses INPUT instead of aritmetic operation, the calculator will display ":" anounciator. In order to hide this effect, the user 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

Infix notation

Infix notation is the common arithmetic and logical formula notation, in which operators are written infix-style between the operands they act on . It is not as simple to parse by computers as prefix notation or postfix notation Infix notation is the common arithmetic and logical formula notation,...

rather than RPN, which most HP scientific calculators use.

External links

• http://www.voidware.com/calcs/hp20s.htm
• HP-20S on MyCalcDB (database about 70's and 80's pocket calculators)
• HP-20S on Porter Electronics (Website where they are still available)
• HP-20S on CalculatorSource (Website where new HP-20S can still be bought)

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