A large number of variables need to be considered and the data to consider these is usually captured on monitoring systems, such as SCADA (Supervisory Control and Data Acquisition).
Mae angen ystyried nifer fawr o newidynnau ac fel arfer mae'r data i'w hystyried yn cael ei ddal ar systemau monitro, fel SCADA (Rheoli Goruchwylio a Chaffael Data).