Abstract: A device for detecting hidden cracks in a structure includes a hand-held probe which is moved over the surface of the structure. The probe is connected to a computer terminal which also has connected thereto a monitor and a keyboard. Changes in the eddy currents in the underlying structure generates impedance changes in the coils of the probe. The resulting voltage values produce an image of the underlying structure and any cracks therein on the computer monitor. The system utilizes a number of procedures to compensate for liftoff problems, imbalance between coil channels, and differences in impedance reference values.