You can get close if you know what type of screws are used. For example if the are adjustment screws are 10-32's, the 32 denotes 32 threads per inch. So one turn on the screw would equal .03125 of an inch or a quarter of a turn would be .00781 of an inch. Like shaneH says if the end of the screw that is pushing against the fin is beveled then that would throw it off a bit. Always use a caliper to zero it in!