The wholesale market for electricity operates under the Electricity Industry Participation Code (EIPC), and is overseen by the market regulator, the Electricity Authority. Trade takes place at more than 200 pricing nodes across New Zealand. Generators can make offers to supply electricity at grid injection points, while retailers and some major industrial users make bids to withdraw "offtake" electricity at grid exit points. The market uses a locational marginal pricing auction which takes generators' offers and retailers' bids, and computes final prices and quantities at each node. These auctions are held every half-hour for a total of 48 trading periods each day.