As pointed out earlier, for small enough Ds the lines of action of the unit vector and will intersect to form a plane as shown in figure. This plane becomes osculating plane as → 0. Now in this plane, draw normal lines to the aforementioned vectors at the respective positions s and . These lines will intersect at some point O, as shown in the diagram. Next, consider what happens to point O as → 0. The limiting position arrived at for point O is in the osculating plane and is called the center of curvature for the path at s. The distance between O and s is denoted as R and is called the radius of curvature. Finally, the vector , in the limit as → 0, ends up in the osculating plane normal to the path at s and directed towards the center of curvature.