Section 5: Storing and Recalling Numbers and ALPHA Strings69
  2. Press the number keys of the applicable register address (00 through 99). Addresses must be 2 digits, e.g., 01, 02, or 50.
For example, to recall the distance to Andromeda’s Great Spiral stored in register R12:
Keystrokes Display    
RCL   RCL _ _   The HP-41C prompts: Recall from which register?
12  2,200,000.0000   The function is performed when the second digit is entered. The distance to Great Spiral is now in the displayed X-register.
g CLX   0.0000   Clears the displayed X-register.
Recalling a number into the X-register causes the stack contents to lift. That is, previous X value is lifted into the Y-register, the previous Y into the Z-register, the previous Z into the T-register. The previous value in the T-register is lost off the top of the stack.
Storing and Recalling in Stack Registers
Using the HP-41C, you can even store and recall numbers into and from the stack and LAST X registers. All you have to do is press · (decimal point) and X, Y, Z, T, or L (for LAST X) as the register address. When the HP-41C prompts you for the address, simply press the associated letter key (X, Y, Z, T, or L)—there is no need to enter ALPHA mode. For example, to store the number 19 into the Z-register of the stack:
Keystrokes Display    
19  19 _   The number is in the X-register.
STO   STO _ _   The HP-41C prompts: In which register?
·   STO ST _   Now the HP-41C prompts: In which stack register?
Z  19.0000   The number is stored in the Z-register.
g CLX   0.0000    
Now, recall the value from the Z-register:
Keystrokes Display    
RCL   RCL _ _   The HP-41C prompts: From which register?
·   RCL ST _   Now the prompt is: From which stack register?
Z  19.0000   The number is recalled form Z.