This guide applies to liquid-immersed-power and distribution transformers, dry-type transformers, and stepvoltage regulators. Additionally, it applies to both single- and three-phase transformers. The purpose of the guide is to: a) Describe the basis and methodology by which the accuracy requirements of (Clause 8 and Clause 9) of IEEE Std C57.12.90-1999 for liquid-immersed transformers and IEEE Std C57.12.91-2001 for dry-type transformers can be achieved. b) Explain why the test code specifies certain procedures and limits. c) Explain advantages and disadvantages of different test methods where alternative methods are available. d) Explain practical limitations and valid means of overcoming them. e) Give theoretical basis for interpolation/extrapolation of tested data and valid limits. f) Explain test anomalies—how they result, what they mean, and how to handle them. g) Give procedures for calibration, certification, and traceability of measurement processes to reference standards. h) Discuss procedures for grounding, shielding, safety precautions, etc. i) Provide schematics and examples to clarify concepts and demonstrate methodologies. New IEEE Standard - Superseded. Information and general recommendations of instrumentation, circuitry, calibration, and measurement techniques of no-load losses (excluding auxiliary losses), excitation current, and loadlosses of power and distribution transformers are provided. The guide is intended as a complement to the test code procedures given in Clause 8 and Clause 9 of IEEE Std C57.12.90-1999.