Based on a literature in non-destructive testing of thin metal films, the fundamental principles for constructing a computerized measurement system operating under personal computer control are examined. The core principles of ECT design are discussed, and the construction of a developed surface-mounted transformer-type miniature ECT with a ferrite core for investigating of films is described. The block diagram and operational algorithm of the measuring system are provided, along with the characteristics of its primary hardware components. The software's operational logic, which controls the system and handles data processing and user-friendly visualization, is thoroughly explained. A technique has been devised to assess the ECT signal's variation rate, allowing precise quantification of flaw sizes and structural inconsistencies in thin metallic layers. Using this proposed method, studies of a film were conducted, demonstrating significantly improved accuracy in defining defect boundaries and dimensions through analysis of the ECT signal change rate. The accuracy increased by up to 7% compared to analyzing direct changes in ECT signal amplitude. © 2025 SPIE.