LOCK BACKSET 2 3/4 or 2 3/8 ?

have wonder about the backset of a lock is it a simple way to check, measure from the frame to the center hole on your meter it will either say 6 or 7 which it 60 or 70 in other word many locksmith will know the measurement by 2 3/4 70mm which is standard length of today door and older style doors they used to make 2 3/8 60MM