Then, subtract the mean from each number in the data set, square the differences, and add them all together. On the Solaris platform, a design limitation currently prevents the tool from determining if a multipatch is closed, resulting in volume measurements being calculated for all multipatches under the assumption they are closed. To calculate a Z score, start by calculating the mean, or average, of your data set. An open multipatch feature will return a value of 0.0. Volume can only be computed for closed multipatches.