An apparatus for evaluating layers 42, 44-48, including interlayer gaps 43, in a multi-layer Structure 40; the multi-layer structure presenting a plurality of edges generally aligned athwart an axis 52; the apparatus 10 (fig. 1) includes: (a) a sensing unit 30, 54 configured for sensing at least one parameter; (b) a positioning unit 22 coupled with the sensing unit; the positioning unit configured to move the sensing unit generally along the axis; and (c) a control unit 16 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. The apparatus may measure thickness of the interlayer gaps or measure thickness of the material layers. The sensing unit may comprise an eddy current coil and the parameter sensed may be impedance experienced by the eddy current coil.
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