PLCalc

The PLCalc application was designed to be a powerful scientific / financial calculator.

The PLCalc calculator uses RPN (Reverse Polish Notation), an architecture made famous by Hewlett-Packard (there is no connection between PLCalc and HP). RPN has many advantages over algebraic calculators, but there is a learning curve for the uninitiated.

To multiply 7 by 9 in an algebraic calculator, one might proceed thus:

Press 7 Press * Press 9 Press =

In RPN, the same operation looks like this:

Press 7 Press Enter Press 9 Press *

The above example is meant only to show the procedure, not the advantage RPN has over algebraic calculators. For that, we turn to a more complex problem. In this example, we need to divide the result of two additions:

y = (a + b) / (c + d)

In this example, the operations are performed in a counterintuitive order, which would require quite a lot of manipulation in an algebraic calculator. But using RPN, it's easy:

Enter a Enter b Enter + Enter c Enter d Enter + Enter /

You may have noticed that in RPN, mathematical operators always follow the numbers. Another name for RPN is "postfix," meaning the operators always follow the values to be operated on.