Calculator RPN

RPN is the name of a type of math entry system used by some calculators. It uses your knowledge of simple algebra as you enter an equation.

The calculator employes a stack, which contains your data. You may think of the stack as, say, pieces of paper, positioned one above the other. This stack rises and falls automatically. The first few stack names are 'x', 'y', 'z', & 't'; but this is not the limit of the stack. It is only limited by calculator memory.

The immediate stack names (i.e., the ones mentioned above) correspond to keys on the calculator. The y^x key gives you the value in stack position 'y' raised to the power of 'x'. The result is placed in 'x'.

Similarly other typical operations are addition ('y' + 'x', with the result placed in 'x'), subtraction (here 'y' - 'x', with the result placed in 'x'), and division is 'y' / 'x', and again the result is plaecd in 'x'.

Here is a simple example equation, just to give a feel for RPN entry...

Here is one way I could approach this equation:

I see a fraction; I'll begin with the numerator. In the numerator I see addition of two parts. I choose to begin at the left; I enter the number 4. This places a 4 in stack position 'x'. Next I enter a 2. The number in position 'x' is moved to 'y', and the 2 is placed in 'x'. The y^x key gives me 4 squared in stack position 'x'.

Next I enter a 4. The value in position 'x' is moved to 'y', and the 4 is placed in 'x'. Next enter a 5. Values in all stack positions move up (to the limits of the calculator's memory), and the 5 is placed in 'x'. Enter divide. Thus the completed part in parenthensis in the numerator is in stack position 'x'.
Remember, there is part of the equation (at this point 4 squared) in 'y' as well; press plus. This gives 'y' + 'x', with the result placed in 'x'.

Next we have the denominator; enter the number 3. Values in all stack positions are moved up, and the 3 occupies 'x'. Enter a 2. Values in all stack positions are again moved up (the stack can at times grow to quite a size...). Next enter a 3. Thus 'y' = 2, and 'x' = 3. Press y^x, and 2 raised to the power of 3 is placed in 'x'. 'y' contains the 3 we entered as we began working with the denominator. Press multiply; the result is placed in 'x'.

Note the entire numerator was raised in stack levels as work was done on the denominator, but not dropped or lost; it is now present in 'y'. Press divide, and the completed equation, or 0.7, is placed in 'x'.

You quickly get a feel for RPN entry, because all you are doing is applying simple algebra to decide which operations to perform on numbers in the stack. It becomes second nature. I was told by the salesperson who sold me my first RPN calculator that once anyone uses one they don't want to use any other type; they are quite nice. But there is a learning curve...

For me she was right on the money; I find RPN an excellent way to manage equation entry.