You set the weights for how a position should be evaluated, and from then on, the current and overall scores that you see for any player at said position will be calculated based off of YOUR determined values.
IE You have two players on your team at LT listed as a 75/75 and 68/68. You change your player weights for the LT position to better emphasize a certain attribute, such as run blocking. Now you review your roster to find that the first LT has changed in rating to be a 78/78 and your other has dropped in value to 66/66. If you re-set the values back to their original setting, you'll see those two player's overall value return to what it was.