From the International Electrotechnical Commission webstore:
“IEC/TS 60076-19:2013, which is a Technical Specification, illustrates the procedures that should be applied to evaluate the uncertainty affecting the measurements of no-load and load losses during the routine tests on power transformers. Even if the attention is especially paid to the transformers, when applicable the specification can be also used for the measurements of reactor losses, except large reactors with very low power factor.”