Section 3: Automatic Memory Stack and ALPHA Register50
 Keystrokes Stack Contents
 + T 0.0000 59 and 19 are added together. Z 0.0000 The answer, 78, is in X and the Y 0.0000 display (Displayed) X 78.0000 53 T 0.0000 53 is keyed in and the 78 Z 0.0000 is automatically raised into Y. Y 78.0000 (Displayed) X 53 + T 0.0000 78 and 53 are added together. Z 0.0000 The final answer, 131, is in X and Y 0.0000 the display. (Displayed) X 131.0000
After any calculation or number manipulation, the stack automatically lifts when a new number is keyed in. Because operations are performed when functions are pressed, the length of such chain problems is unlimited unless a number in one of the stack registers exceeds the range of the calculator (up to 9.999999999 × 1099). When the range of the calculator is exceeded, the HP-41C immediately indicates OUT OF RANGE in the display. Later you will learn how to instruct the HP-41C to ignore these types of overflows.
In addition to the automatic stack lift after a calculation, the stack automatically drops during calculations involving both the X- and Y-registers. It happened in the above example, but let’s do the problem differently to see this feature more clearly. For clarity, first press g CLX to clear the displayed X-register. Now, again solve 21 + 38 + 19 + 53 = ?
 Keystrokes Stack Contents
 21 T 0.0000 21 is keyed in. Z 0.0000 Y 0.0000 (Displayed) X 21 _ ENTER T 0.0000 21 is copied into Y. Z 0.0000 Y 21.0000 (Displayed) X 21.0000 38 T 0.0000 38 is keyed in. Z 0.0000 Y 21.0000 (Displayed) X 38 _