The table shown here summarizes the past performance thresholds established over time, up to Level V. The internationally approved test method for determining efficiency has been published by the IEC as AS/NZS 4665 Part 1 and Part 2. The approach taken to establish an efficiency level is to measure the input and output power at four defined points: 25%, 50%, 75% and 100% of rated power output. Data for all four points are separately reported as well as an arithmetic average active efficiency across all four points.