How to use an RPN Calculator

To add 2 and 5 on a normal calculator, you type "2 + 5 =". But what if you want to add 2, 5, 8, 6, and 4, and then divide that sum by 5? Then it's not so simple. Both operations are easy on an RPN Calculator. In RPN, you have a stack you can place numbers on, and then you do math on the numbers on the stack. The basic opperation is "place 2 and 5 on the stack, then add them." If you look at the image above, you'll probably recognize many of the buttons. The new one that should jump out at you is the large "enter" key. Enter is how you get numbers onto the stack. Where you'd do 2 + 5 = on a normal calculator, in RPN you'll instead do:

2 enter 5 +

The + takes the last two numbers from the stack, adds them together, and then puts the sum back. This lets us do some neat things, like that average operation I mentioned previously. To do (2 + 5 + 8 + 6 + 4) / 5 do this:

2 enter 5 enter 8 enter 6 enter 4 + + + + 5 /

In other words, enter the 5 values on the stack and add them together. Now the sum is on the stack. Enter 5 and divide the sum by it. Try it once or twice and things should start to make sense. The stack can hold as many numbers as you want, but you can only see the last 9. If you enter more than 9 numbers, the oldest ones fall off the screen, but are still there waiting for you to get to them.

There's one more major difference between an RPN and a normal calculator. You'll notice that there's no "clear" button. Instead use the "drop" button to drop the last number from the stack. To clear everything on the stack, hit drop a bunch of times.

That's RPN Calculating in a nutshell, but here are a few more hints.
Hitting enter a second time duplicates the last item on the stack.
The "swap" key swaps the last two numbers on the stack.
The "roll" key takes the last number on the stack and moves it all the way to the back.

I hope this gives you enough information to get started. With some expirimentation, I'm sure you'll get the hang of it. With a little use, I'll bet you'll find that you really like this style of calculating.

RPNCalc Page