A measuring instrument (10) for contactless ascertainment of a rotation angle is made up of a support plate (12) that is comprised of magnetically nonconductive material and serves as a rotor. A permanent magnet (15), which is embodied as planar, is disposed on the support plate (12) and its polarization direction is aligned diametrically to the axle (11). If the Hall element (20) is asymmetrically disposed, i.e. if the Hall element (20) describes an elliptical rotary motion in relation to the permanent magnet (15), then a steeply decreasing region and a flat region are produced in the curve of the output signal. No magnetic flux conducting parts are required in the measuring instrument (10). Furthermore, it is very small and relatively easy to incorporate into systems and devices.