## Why RPN?

Reverse Polish notation (RPN) is a mathematical notation in which every operator follows all of its operands. It is also known as postfix notation. Used in a calculator it has the great advantage that it does not need any parentheses. This leads to faster calculations and fewer mistakes. It takes a little time to get used to but after that you will love it. If you want to know more on the background of RPN and the history of Hewlett-Packard calculators, have a look at this Wikipedia article.

## Select RPN-mode

To work with RPN you can switch to RPN-mode by pressing `j`

, or use the Options menu. As you can see the Operations stack has disappeared as you don't use it in RPN-mode. In RPN-mode the content of the stack is remembered on your computer.

## RPN by example

Suppose you want to calculate 34 x 42. There you go: `34 Enter 42 *`

, et voila. Now suppose you have to calculate 34 x (42-19). Just work your way from left to right: `34 Enter 42 Enter 19 - *`

. As you can see intermediate entries or results are placed in the stack. To make it a bit more complicated take the following.

```
88 - 23
------------
52 + 6^0.4
```

Just work your way from left to right and from top to bottom: `88 Enter 23 - 52 Enter 6 enter 0.4 y + /`

.

In the history stack you can see what you have done and check if you didn't make a typing error. The final expression has to be (88-23)/(52+6^0.4). To drop (clear) the stack press `d`

or `c s`

for the complete stack.

The calculator uses the dot as the decimal point, but you can change that to comma in the Options menu (`o`

). To enter negative numbers: enter the number and then press `n`

to change the sign. The calculator also accepts numbers in scientific notation. Use `e`

to enter exponent; `Shift-e`

or `- e`

for negative exponents.