This System Workload Power Measurement Methodology Team has published a methodology that supports architectural analysis and comparative measurements for rankings, such as the Top500 and Green500. To support measurements with varying amounts of effort and equipment required we present three distinct levels of measurement, which provide increasing levels of accuracy.
Level 1 is similar to the Green500 run rules today, a single average power measurement extrapolated from a subset of a machine. Level 2 is more comprehensive, but still widely achievable. Level3, the "current best," is only possible at a few sites but generates a high quality result which exposes details the others may miss.