0 - 1 of 1 tags for stored procedure variables

Hi -
Can someone help me understand if the values in the variable change when the values in the source changes?
 
Sample Tbl1 Data:
Fld1
1
 
Sample Tbl2 Data:
Fld1     Fld_X
1         ABC
2         XYZ
 
To explain it better, here is the sample SQL:
SELECT Fld1