All inspection systems have advantages and disadvantages when compared to each other. The most important advantage of the Therm-O-Matic® is the linear relation between defect signal Δt and defect depth. Detailed research and test works enabled us to establish the effect by factors influencing the amplitude of the defect signal Δt and find technical solution to set, measure and adjust these parameters. The defect signal Δt is kept independent of speed, product dimension, product shape, coil size and surface temperature by continuous control of the process as the product goes through the installation.