A ring magnet for use in determining a rotational angle of a rotatable shaft and configured to be connected to the rotatable shaft for co-rotation with the rotatable shaft around a rotational axis may include a recess in a circumferential surface of the ring magnet, where the recess may be recessed away from the circumferential surface to cause a magnetic sensor to measure a substantially constant ellipticity of a radial component of a magnetic field of the ring magnet and a tangential component of the magnetic field of the ring magnet, when measuring the rotational angle of the rotatable shaft, as the ring magnet moves along the rotational axis of the rotatable shaft.