Open-outcry is the oldest way of trading on the exchange, though nowadays the majority of trades are placed electronically. It is central to the process of price discovery, the way LME official prices are established. Prices are derived from the most liquid periods of trading; the short open-outcry ring trading sessions, and are most representative of industry supply and demand. The official settlement price, on which contracts are settled, is determined by the last offer price before the bell is sounded to mark the end of the official ring.