The interval class vector is a listing of the ic content of a given pc set. This is an ordered listing of the number of representatives of each interval class contained within the set. [100110] is an ic vector (for pc set {1,2,6}) that indicates this set contains one representative each of ic1, ic4, and ic5, and no representatives of ic 2, ic3, and ic6.

To calculate the interval class vector for a given set, carefully study the following procedure. This process should be done using either the normal order or the prime form of the pc set. Essentially, you create a "triangle of differences" by subtracting each pc in the set from the remaining ones. Given the pc set {1,2,3,6,7}, the interval class vector for this set would be calculated as follows:

1.subtract the first pc from those to its right:  1  2  5  6
2.subtract the second pc from those to its right:    1  4  5
3.subtract the third pc from those to its right:        3  4
4.subtract the fourth pc from those to its right:          1

Next, determine the number of representatives of each ic contained in the "triangle of differences" (count how many of each different number). There are: 3 ic1, 1 ic2, 1 ic3, 2 ic4, 2 ic5, and 1 ic6. Therefore, the interval class vector for the pc set {1,2,3,6,7} would be [311221]. Note that the ic vector is notated using square brackets and no commas between the numbers.