Data from the Eddy Current testing (ECT) by Bobbin probe at various frequencies (Start-End) show a defect on the outer surface (OD) of the measured steam generator tube from NPP Bohunice V1. The eddy current signal is visualized as: a) a linear progression over time of individual signal components with the axial position of the indication, and b) the display of indication in the X−Y plane (a complex impedance plane). The parameters of indication for the main measurement frequency f=200 kHz are A=4.89 [V], phase = 87 [°], wall thickness loss = 70%. Peak-to-Peak Voltage (Vpp) measurement mode used.