Can be considered the amplitude of total head movement asymmetry, taking into account both Diff Max and Diff Min of the head.
As the side and timing of forelimb lameness is dependent upon both Diff Max Head and Diff Min Head, this single variable can be more easily used to estimate the overall level of forelimb lameness.
Total Diff Head is the Vector Sum of the mean Diff Max and mean Diff Min values, and is calculated using Pythagorean Theorem (a2 + b2 = c2), where a is the value of Diff Max head, b is the value of Diff Min head, and c is Vector Sum. (a) is plotted on the X axis, (b) is plotted on the Y axis, and the hypotenuse that forms that triangle is the Vector Sum. Total Diff Head is indicated by the RED ray on the forelimb plot.
The Total Diff Head (Vector Sum) reference range is 0 to 8.5mm. The upper reference range value of 8.5 is derived from the VS calculation when Diff Max Head and Diff Min Head are at their upper reference range values of |6|. 62+62=VS2