Section 3: Automatic Memory Stack and ALPHA Register51
Keystrokes Stack Contents    
ENTER   T  0.0000   38 is entered into Y.
  Z  21.0000   21 is lifted up to Z.
  Y  38.0000    
(Displayed)  X  38.0000    
19 T  0.0000   19 is keyed in.
  Z  21.0000    
  Y  38.0000    
(Displayed)  X  19 _    
ENTER   T  21.0000   19 is copied into Y.
  Z  38.0000   21 and 38 are lifted up to T and Z
  Y  19.0000   respectively.
(Displayed)  X  19.0000    
53 T  21.0000   53 is keyed in.
  Z  38.0000    
  Y  19.0000    
(Displayed)  X  53 _    
 +   T  21.0000   19 and 53 are added together and the
  Z  21.0000   rest of the stack drops. 21 drops to Z
  Y  38.0000   and is also duplicated in T. 38 and 72
(Displayed)  X  72.0000   are ready to be added.
 +   T  21.0000   38 and 72 are added together and the
  Z  21.0000   stack drops again. Now 21 and 110
  Y  21.0000   are ready to be added.
(Displayed)  X  110.0000    
 +   T  21.0000   110 and 21 are added together for the
  Z  21.0000   final answer and the stack continues
  Y  21.0000   to drop.
(Displayed)  X  131.0000    
The same dropping action also occurs with  –  ,  ×  , and  ÷  . The number in T is duplicated in T and drops to Z, the number in Z drops to Y, and the numbers in Y and X combine to give the answer, which is in the displayed X-register.
This automatic lift and drop of the stack give you tremendous computing power, since you can retain and position intermediate results in long calculations without the necessity of reentering the numbers.