Compasses that do more than point north are used in several sciences, especially the earth sciences. These compasses measure the orientation of two- and three-dimensional objects. One such measurement is the dip of an object, its tilt with respect to a horizontal surface. Compasses designed to measure dip include a clinometer, a bubble level mounted on a pivot to measure inclination. Most compasses with a clinometer also have a bull's-eye level for measuring the strike, or the bearing of the intersection of a surface with a horizontal plane. This information is needed to measure the true inclination.