Erik Østergaard  Four Function RPN (Reverse Polish Notation) Calculator / Fire funktions RPN regnemaskine 
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This calculator uses postfix notation, and works a little differently from calculators you may have used. Suppose you want to add two numbers. Enter the first number. Press "Enter." This commits the first number into the calculator's memory. Then enter the second number. After that, enter the type of operation (such as "+") that you wish to perform. Use only the period (.) as a valid decimal separator.
This is a demonstration RPN (Reverse Polish Notation) calculator implemented in JavaScript. You must have a JavaScriptcapable browser for this to work. Note that keyboard entry is disabled in this demo.
The Four Function RPN Calculator is a Javascript Program  adapted from a sample calculator Javascript app from Dave Steele. You can see the JavaScript by using View Source.
