Method of calculating other body measurements from chest measurements

Using chest measurements we can calculate other upper body measurements.This is for standard body measurements.But to get good measurement it is good to take measurement of each part.
Neck= ⅓ chest + 2½"
Waist =chest -5 to 7 "
Seat = Chest + 2 to 4"
Across chest  = ⅛ th chest + 2¼"
Half back =⅙ th chest + 1"
Half shoulder =⅙ th chest 1½ to 2"
Upper arm or biceps =  ¼ chest + 2 to 2½"
Scye depth =⅛ th chest +  2 to 2½"