However, whether the latter is mainly aimed at identifying supply shortages, the indicator at hand is aimed at discovering temporary oversupply. Whether or not this situation may occur, depends on the flexibility of the power system as a whole, i.e. flexibility on the supply side (shutdown and ramping capabilities of generation units) and demand side (interruptible contracts, variable pricing, smart metering, etc.). The flexibility of the demand side of the power system will be dealt with in more detail under demand-side security of supply indices. This is particularly relevant when extreme events occur, occasioning sudden decreases in demand or increases in supply from other sources.