Statistic amount got from two groups of variables, named A and V, through summing formula X(.V,-.V)(>',-?), where X stands for the mean value of X, and V' stands for mean value of V.
SUM OF CROSS PRODUCTS: "Example: Sum of cross products for the data 1 3, 4 6, 7 9, 1 1 is: 1x3+4x6+7x9+1x1=91"
