Abstract: An apparatus for determining magnetic properties of a portion of a magnetizable endless belt. The apparatus includes a primary coil for generating a magnetic field. The windings of the primary coil are wound around the endless belt. A secondary coil measures the magnetic flux density. A slotted yoke guides the magnetic flux. The endless belt extends through slots in the yoke. First measuring devices measure the magnetic field in a width portion parallel to the endless belt. Second measuring devices measure the magnetic field in the width portion parallel to the endless belt.