The ART-3D™ series of ratio meters are high precision instruments, designed to measure turn ratios, phase displacements, excitation currents of single phase and three phase power, distribution and instrument trans- formers in conformity to the IEEE C57.12.90 & IEC 60076. With its real 3-phase test circuit, the ART-3D™ can address complex ratio measurements of Phase- Shifting/ Regulating or irregular vector group type transformers, otherwise impossible to achieve with conventional ratio meters.