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 _