This invention provides a method and an apparatus for use in controlling a nip through which material is passed. The apparatus comprises at least one means for generating a magnetic field and means for locating the magnetic field generating means at a selected position along the length of one of the pressing elements, adjacent to the element, to thereby affect only a portion of the length of the element thus controlling only that portion of the length of the nip which is generally aligned with the affected portion of the pressing element.