But is the curvature where is the radius of curvature. So rewrite the differential equation as , which gives the radius of curvature at a point on the curve as a function of the angle .

From this, the following approximate construction is possible: at the initial point construct the tangent of slope , and on the perpendicular line to it take a point at distance from . Construct an arc of angle with center at and initial point . The endpoint of the arc is , which is the approximate second point on the curve. (The points determine the evolute of the curve, approximately.)