What the heck?

You have just installed this new, shiny app and are eager to test it. At first, you try something easy; 2 + 3 = 5 perhaps? So you type "2", then "+", then "3"... Ahem, something strange shows on top: "0+2" (?). And where is the "=" button? What the heck?

This calculator uses Reverse Polish Notation (postfix, RPN) instead of the ususal algebraic (infix) notation used by most other calculators. No, don't give up yet; it's easy: first, hit the "C" button to clear the screen, then enter "2" followed by the "Enter" key, then "3" followed by the "+" key. Here is a shorthand for this:

2 EN 3 +

The top display now shows "2+3" while the main display features "5". Good.

RPN is one of many calculator input methods. In it, operands (that is 2 and 3 in our example) are entered before the operation (+). Why, in the world, would anyone do that? Simply, RPN lets one enter very complex mathematical expressions without parentheses and with minimal number of button presses. It is very efficient. Please notice that the app's keyboard neither has parenthesis buttons, nor the usual "memory" buttons; the "M+", "M-", etc., ones. These are not needed! James Redin posted a very nice web page illustrating advantages of RPN with more examples. Go ahead, try something more complicated: evaluate [(8+6)(7-5)+(4-2)]/[(9-7)*(1+2)-3]:

8 EN 6 + 7 EN 5 - * 4 EN 2 - + 9 EN 7 - 1 EN 2 + * 3 - /

Have you noticed how the app automatically figured out all the needed parentheses and showed all the partial results on the way? That's pretty cool! All in only 26 keystrokes. Try it with an algebraic calculator without writing down or memorizing partial results. The top display now shows the complete expression:

while the main display shows the final result of "10". Turns out, the third pair of parentheses was not necessary.

With minimal practice you will become quite proficient at RPN, I promise. The Tutorial and Formula Examples sections of this manual contains plenty of examples to learn from.

If you are technically inclined, then you probably know that the success of RPN is intimately tied to a programming object called stack. This calculator features an unlimited stack that you can display at any time - just tap the top display and it should change into the following view:

Contents of the stack resembles the sequence of keystrokes you entered above, except the omitted "Enter" presses. The latter can be identified when any two numbers neighbor each other. If you study computer science, then this little feature may come quite handy in learning about stacks and recursion. Go ahead, draw a recursive binary tree for this stack and compare it to the original expression. How do parentheses relate to it? Tap the top display again to go back to the expression.

One more thing: you can e-mail these help pages to yourself at any time for either printing, or displaying on your computer screen. Just hit the "Compose" button in the right lower corner of the apps Help screen.