Abstract: This invention relates to methods and apparatus for inspecting surfaces such as plates or pipe walls of magnetisable material using magnetic reluctance to gain data about the surfaces being inspected. In a preferred method, a magnetic circuit that passes through at least a magnetising unit and a portion of the surface to be inspected is created. The magnetic reluctance in the magnetic circuit is measured at one or more positions in the circuit. At least one of the measured magnetic reluctance values is incorporated into one or more algorithms. The result of the or each algorithm is recorded or displayed for each magnetic reluctance reading in association with information concerning the position of the or each magnetic reluctance reading on the surface.