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Fig. 2. Graph (based on the 10° simulation) to show the important features of
the horizontal or x position during contact time. The deviation from
the position that would result from constant velocity (i.e. a straight line)
has been magnified x15 to demonstrate the fluctuation in speed through
stance. The gradient of the line at times 0 and Tc are
equal and the gradient is at a minimum at midstance.