Method and apparatus for locating non-visible objects

An apparatus for locating non-visible objects positioned behind an opaque surface, such an object being in use operable to generate a magnetic field variable with physical location, which apparatus comprising:

• a base member adapted to be placed on or against the surface;
• means in the base member defining a machining guide;
• an array of magnetic field strength sensors being associated geometrically with the machining guide, such that the machining guide and the array of sensors are fixed positionally one relative to the other;
• means for collecting and analyzing outputs from at least some of the sensors to provide an indication of the variation of the magnetic field associated with the object relative to the position of the base member, wherein the means for collecting and analyzing outputs is operable to determine the displacement between the object and the machining guide;
• and
• means for enabling moving of the array and machining guide by means of manual control based on the determined displacement such that once the machining guide is located immediately and centrally over a point on the opaque surface that is opposite the object lying behind, the position of the array and machining guide is fixed during a mechanical operation;
• wherein said fixing is effected by a fixing means for locking the array onto the surface via vacuum pads at one of two levels of holding force, one level providing a sufficient holding force to attach the array and machining guide to the surface sufficiently loosely for the performance of said moving, and another holding level at which the array and machining guide are firmly clamped in a fixed position against the opaque surface.