# Calculator Basics - RPN

You can configure the calculator to use Reverse Polish Notation (RPN) using the calculator "opt" button and selecting the "mode" tab. This gives you the option of selecting algebraic logic (the default), "as entered" (arithmetic operators are applied in the order entered regardless of the rules of operator precedence) or RPN.

The layout is very similar to the algebraic logic mode. Instead of the "=" button there is a button marked "Ent" for "Enter". The memory buttons are now called "STO" (store) and "RCL" (recall) and pop up a dialogue box to select the memory number. There is a button "CLx" which clears the value at the top of the stack, and "REG" which clears all the registers.

Example:
1 Ent 2 Ent 3 Ent 4 Ent would push the values 1, 2, 3 and 4 onto the stack
Repeatedly pressing the + button would pop each value off the stack in turn, adding it to the total, finally resulting in the answer 10.

If you click on the button you get three further RPN functions. The button allows you to view the contents of the stack (because of the way the internal logic works you will see the top of the stack (or X) in positions 0 and 1). If you click on one of the numbered buttons, the corresponding value will be added to the top of the stack.

There is an button which switches the top two values in the stack. And the stack roll down button will pop a value off the stack and move all the other values up.