With the Rockwell 6S and 6C, the plates are what determine the shave setting. The number on the plate at the bottom of your razor is the shave setting you are using. 

For the Model T, choose your preferred setting and simply adjust the setting using the dial on your handle. 

Keep in mind that setting one creates the mildest shave while setting 6 offers the closest shave. We always recommend starting with mild settings (R1-R3) and working your way up to a higher setting if you need to.