PPT Slide
In general, a grain boundary has five degrees of freedom.
We need three degrees to specify the orientation of one grain with respect to the other, and
We need the other two degrees to specify the orientation of the boundary with respect to one of the grains.
Grain structure is usually specified by giving the average diameter or using a procedure due to ASTM according to which grains size is specified by a number n in the expression N = 2n-1, where N is the number of grains per square inch when the sample is examined at 100x.