About CalcIT RPN


The CalcIT calculator is a simple Reverse Polish Notation (RPN) style calculator. More information about the RPN method is available at Wikipedia.

The Basics of RPN:

RPN is the same as how you normally do calculations on paper. You write down the numbers then do the math.

To use an RPN calculator:

  1. 1.Enter the first number

  2. 2.Hit the “ENTER” key

  3. 3.Enter the second number

  4. 4.Hit a math function key (+,-,x, or ÷)

  5. 5.Result is displayed.

The CalcIT RPN calculator uses a register stack to store up to four numbers in memory (registers x, y, z, and t), including the main display (register x).  This allows  more complex calculations to be performed without storing the intermediate results in a memory or using parenthesis as on non RPN scientific calculators.

For example:

  1.     95 + (5.5 x 6)
         ( 3.5 + 12.5)

would be calculated as follows:

  1. 1.Enter “95”

  2. 2.Hit the “ENTER” key

  3. 3.Enter “5.5”

  4. 4.Hit the “ENTER” key

  5. 5.Enter “6”

  6. 6.Hit the “x” (multiply) key

  7. 7.“33.0“ is displayed

  8. 8.Hit the “+” (add) key

  9. 9.“128” is displayed

  10. 10.Enter “3.5”

  11. 11.Hit the “ENTER” key

  12. 12.Enter “12.5”

  13. 13.Hit the “+” (add) key

  14. 14.“16.0” is displayed

  15. 15.Hit the “÷” (divide) key

  16. 16.Result is “8.0”

How the Memory Stack Operates:

Notice how the numbers move up the stack when the “ENTER” key is pressed and down the stack when a math operation key is pressed.   If you ENTER several numbers, the top number will drop of the top of the stack.  As math keys are hit one after the other, the calculations are performed on the “x” and “y” registers and


CalcIT RPN Calculator

numbers stored in registers z and t drop down the stack in order.  The top or “t”  register, will eventually get copied down until all the registers contain the original “t” register value. 

If you wanted to see a sequence of numbers such as the powers of 2, you would enter the number 2 in all the registers, then keep hitting the multiply “x” key (multiply) to get 2, 4, 8, 16, 32, 64, etc.

Function Keys:

  will roll the main display and the registry displays through the stack.

  switches the x and y registers.

  changes the sign of the number in the display (x register).

Scientific Functions:

CalcIT provides basic trigonometric functions including degree/radian conversion.  It also has square root, square, and temperature conversion.  

will display the buttons for trigonometric and other functions.  The red “x” button is pressed to close the view or the “f” key is pressed again.

How to Clear the Registers and Screen:

Swipe each display area horizontally left or right to clear it.


Shake the iPhone to clear  both displays.

Display Settings:

FIX displays numbers with a fixed number of decimal places:  

  1. 235640.00000

SCI displays numbers in scientific notation:

  1. 2.35640E+05

ENG displays numbers in engineering notation:

  1. 235.640E+03


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