Abstract: This paper, in view of the errors in some books, expounds completely the important problem, that the amended modification link make the size of close link large or small.Four cases of the amended modification link which makes the size of the close link large or small are clearly put forward. A series of calculation formulae applicable to minimum modification amount equal to zero or not are systematically deduced. These important formulae of calculating the size of modification link are different from those in many other books, in that they are easy to be grasped and convenient to be calculated.

Key words: 封闭环, 修配法, 修配量