Before attempting an analysis of the alternate striking distance equations, the stroke
angle should be considered. In Young's original derivation of the geometric model,
only vertical strokes were considered. That is, the downward leader was assumed to
be perpendicular to the line, and the previously developed equations apply for these
vertical strokes. Later, Whitehead and his associates developed the concept that the
downward leader could approach the line from any direction and further suggested
the probability density function