Jack wanted to test which brand of car wax was most effectiv…

Jack wanted to test which brand of car wax was most effective on his car paint. He tested four brands of wax. He cleaned the hood of his car and removed the old wax. He measured four equal sections on the hood of the car. Each of the waxes was used to cover a section. An equal amount of wax, the same type of rag, and equal buffing were used. To test their effectiveness, five drops of water were placed on each square, and the diameter of each drop was measured (cm).  Why were an equal amount of wax, the same type of rag, and equal buffing used in the experiment?