Note 1 to entry: If the energy not supplied is expressed in megawatt-minutes, and the annual peak load in megawatts, this index is often referred to as "system-minutes". One minute of this quantity is equivalent in energy to an interruption of the total system load for one minute at the time when the annual system peak load occurs.

Note 2 to entry: The annual system peak load refers to the highest load in that year.

Note 3 to entry: This entry was numbered 191-30-03 in IEC 60050-191:1990.