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This classical problem is dealt with in K. Murphy, H. A. Sabbagh, and J. C. Treece, "Thickness Measurements with Eddy-Current Probes: A Simple Inversion Problem," Review of Progress in Quantitative Nondestructive Evaluation, Vol. 13, edited by D. O. Thompson and D. E. Chimenti, Plenum Press, 1994, pp. 927-934. In that paper, we use experimental measurements, and reconstruct the thickness of a brass plate, together with the probe lift-off, to within a percent, or so. From that work, we conclude that modern computational tools, such as VIC-3D®, provide an excellent means of determining plate thickness from measurements with eddy-current probes. Such tools provide a means of optimizing probe design and measurements to maximize the accuracy achieved. They also provide a means of determining the accuracy in thickness that can be expected from impedance measurements of a given accuracy, or conversely, the accuracy required in measurements to achieve a prescribed accuracy in thickness determination.