The stainless steel ball base is held with the tip (base center) at the object point. With the base contour, curved edges can be detected as well as straight ones. Since the tip of the quadrant is exactly in the center of the base, it can be held at any angle to the edge. For measurements in tracking mode we recommend the base with the weaker magnet, overhead and vertical the base with the stronger magnet. Scope of delivery without 1.5" sphere prism.