An example of number of cluster prediction with the use of G-Gap. The G-Gap Heuristic. The curve in green is a WCSS curve obtained on the CNS Rat dataset with the use of the K-means algorithm. The line in red is obtained by projecting upward the end points of the WCSS curve by a units and then joining them. It is a heuristic approximation of WCSS for a null model. The vertical lines have the same role as in Gap and the rule to identify k* is the same, yielding a value k* = 7, a value very close to the correct number of classes(six) in the dataset.