Technical report. From Abstract : "A number of similar eddy current instruments were developed to measure the thickness of Zircaloy over uranium metal in the range of 5 to 25 mils, Zircaloy over UO2 in the range of 20 to 40 mils, and the wall thickness of Zircaloy tubes in the range of 20 to 40 mils. The instruments were designed for use with hand-held probes or with feeder-mounted probes to measure the inside and outside cladding thickness of tubular elements and the wall thickness of Zircaloy sheaths. The instruments have a sensitivity of 3 microamps per mil change in Zircaloy thickness and an accuracy of +/- mil."