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Programming

How the RPN stack works

Enter numbers first, then the operation. Learn what ENTER, swap and the stack do.

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RPN calculators keep your numbers in a short pile called the stack. You type a number, press ENTER to push it, type the next number, and then press an operation. The operation uses the top numbers of the pile and leaves the answer on top.

There are no brackets and no equals key. Intermediate answers wait on the stack until you need them. To work out (3 + 4) × (5 + 6): add 3 and 4 to get 7, leave it there, work out 5 + 6 = 11, then multiply the two.

RPN Scientific 15

Start on the main screen: There is no menu to leave. Press the back arrow to clear a number you are typing, or CLx (g then back arrow) to clear the X register.

  1. Key in 3, press ENTER to push it up, key in 4, and press + . The 7 sits at the bottom of the stack.

    3ENTER4+

  2. Now work out 5 + 6 the same way. The 7 moves up one place to make room.

    5ENTER6+

  3. Press × . It multiplies the bottom two numbers, 7 and 11.

    ×

You should see77.0000

The display shows four stack levels. The bottom line is X (what you are working on), then Y, Z and T above it.

Press x⇄y to swap X and Y, which is handy for subtraction and division in the wrong order.

RPN Scientific 15 key reference

RPN Financial 12

Start on the main screen: There is no menu to leave: the display always shows the X register. Press f then R/S (P/R) to leave program mode, and clear a pending prefix by pressing ON.

  1. Key in 3, ENTER, 4, + to get 7.

    3ENTER4+

  2. Key in 5, ENTER, 6, + to get 11. The 7 waits on the stack.

    5ENTER6+

  3. Press × to multiply them.

    ×

You should see77.00

RPN Financial 12 key reference

RPN Advanced 42

Start on the main screen: Press EXIT (once or twice) to close any menu and return to the plain stack view of Y and X.

  1. Key in 3, ENTER, 4, + to get 7. The screen shows X (bottom) and Y (above it).

    3ENTER4+

  2. Key in 5, ENTER, 6, + to get 11.

    5ENTER6+

  3. Press × to multiply the 7 and the 11.

    ×

You should seex: 77.0000

RPN Advanced 42 key reference

RPN Power 48

Start on the main screen: Press ON to cancel what you are typing, then use the stack view. Open the MODE or VAR menu any time; the stack is always shown above the menu row.

  1. The Power 48 shows a numbered stack, level 1 at the bottom. Type 3, ENTER, 4, and press + .

    3ENTER4+

  2. Do the same for 5 and 6.

    5ENTER6+

  3. Press × to multiply levels 1 and 2.

    ×

You should see1: 77

RPN Power 48 key reference

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