Without seeing your guitar, I'm going to assume the "tightening lugs" you're reffering to are the string locks on the nut. On a guitar with a "floyd rose" style tremolo system, the strings pass through a clamping system at the nut before going to the normal tuning keys. This clamping system "lugs" must be loosened then the guitar is tuned as it normally would, then the lugs are tightened to lock the strings in place. These clamps are not part of the tuning mechanism, but instead lock down the strings after they have been tuned by the keys. After all that, one would fine tune the guitar at the bridge rather than at the keys. A more complete explaination is found here-
String Tuning Instructions