e develop an evaluation method for form deviation of complex planar curve contours based on coordinate measurement data. Using this method, the contour curve is expressed in terms of its optimal interpolation circular arcs, whore interpolation accuracy can be specified arbitrarily, and the form deviation is defined as the deviation between the points of measurement and the arcs. The difference between both the deviations relative to the contour curve and relative to the arcs is not larger than the circular interpolation accuracy. The geometrical form deviation of the profile is evaluated using the simplex search algorithm based on the minimum zone criterion. An actual evaluation example for a planar cam profile is shown. The form deviations of the cam profile obtained by the present method satisfy the geometrical condition of the minimum zone criterion and are obviously smaller than the ones obtained by the least squares criterion.