Section 3: Automatic Memory Stack and ALPHA Register43
Keystrokes Display    
5.6  5.6 _   The number and _ prompt.
     5. _   One right-most digit deleted.
7  5.7 _   The edited number
        5 _   Delete the 7 and decimal point.
     0.0000   Deleting the last number clears the X-register to zeros.
While you keying in ALPHA, pressing    also deletes one right-most character at a time, but blanks the display when you delete all of the characters. Again, notice the movement of the _ prompt.
Keystrokes Display    
ALPHA ABB  ABB _   The ALPHA string.
     AB _   One character deleted.
C  ABC _   The corrected string.
           _   When the last ALPHA is deleted, the display is blanked, leaving the _ prompt. The stack is not disturbed.
ALPHA   0.0000   Return to normal mode.
To aid in recovering from other keystroke errors,    lets you clear the X-register with a single press.
Keystrokes Display    
2     1.4142   The result.
     0.0000   The X-register has been cleared to zeros (no _ prompt was present).
And to clear a function requiring input:
Keystrokes Display    
RCL   RCL _ _   The function and prompt.
9  RCL 9 _   Whoops, you decided not to do this.
     RCL _ _   The input may be deleted and changed.
     0.0000   Or you may clear the entire operation.
Using    is easy and convenient, and you will learn how    is used in other ways for correction as you continue reading this handbook.