An apparatus for evaluating layers, including interlayer gaps, in a multi-layer structure; the multi-layer structure presenting a plurality of edges generally aligned athwart an axis; the apparatus includes: (a) a sensing unit configured for sensing at least one parameter; (b) a positioning unit coupled with the sensing unit; the positioning unit being configured to effect moving the sensing unit generally along the axis; and (c) a control unit coupled with at least one of the positioning unit and the sensing unit. The control unit provides an electrical signal to the sensing unit. The control unit monitors changes in the at least one parameter as the sensing unit moves past the plurality of edges. The control unit employs the changes in the at least one parameter to effect the evaluating.