As operating time of nuclear power plants increase, corrosion products in secondary water are built up as scaled deposits on the outside of steam generator tubes, increasing potentials for the corrosion of tube materials with fluid flow restrictions and heat transfer efficiency problems. Several experiences in nuclear power plants have shown that the heat fouling by corrosion product formations in secondary side cause water level oscillation, degrading the thermal performance of steam generators. It is necessary to assess the extent and location of scaled deposits on steam generator tubes for the effective management and maintenance of steam generator. In prior work, tube mock-ups with various thicknesses of scaled deposits have been set up to provide information about the overall deposit condition of steam generator tubes, deriving methodologies to automatically measure deposit thicknesses [1]. In this paper, another tube mock-up with different deposit simulation method is used to improve the similarity in deposit densities of field data and eddy current signal behaviors from the new tube mock-up are correlated to the deposit thicknesses. Using the correlation as a reference, the automatic scaled deposit measurement system has been developed with 3 dimensional mappings of deposit distributions and the overall estimation of the scaled deposit amount. The developed system has been applied to actual plant data of 2 outages and showed similarities with heat transfer distributions of steam generators. Historical comparisons of 2 outage data revealed actual increase of deposit formations and provided useful information as an analysis tool for steam generator deposit formation monitoring and maintenance.