STO

On a Casio calculator you can store a value in a variable

RCL

To store the value 123 in variable A

1   2   3        RCL 123_
                  0.    A 123→A
               123.

To store the value 5.2 in variable B

5   •   2        RCL 5.2_
                  0.    B 5.2→B
                5.2