HP 35s HP 35s scientific calculator - User Guide - Page 52

How ENTER Works You know that  separates two numbers keyed in one after the other. In terms of the stack, how does it do this? Suppose the stack is again filled with 1, 2, 3, and 4. Now enter and add two new numbers: 1 lost 5+6 2 lsot T 1 2 3 3 3 Z 2 3 4 4 3 Y 3 4 5 5 4 X 4  5  5  6  11 1 2 3 4 1. Lifts the stack. 2. Lifts the stack and replicates the X-register. 3. Does not lift the stack. 4. Drops the stack and replicates the T-register. replicates the contents of the X-register into the Y-register. The next number you key in (or recall) writes over the copy of the first number left in the X- register. The effect is simply to separate two sequentially entered numbers. You can use the replicating effect of  to clear the stack quickly: press 0 . All stack registers now contain zero. Note, however, that you don't need to clear the stack before doing calculations. Using a Number Twice in a Row You can use the replicating feature of  to other advantages. To add a number to itself, press . 2-6 RPN: The Automatic Memory Stack