The state will select a base year to be used in calculating curtailment targets for individual consumers. Base year and base billing period data may be weather-normalized at each utility's discretion using standard utility procedures, and will be calculated for any consumer audited under this plan. Utilities may elect to audit residential and general use consumers for whom no actual base year or base billing period data exists, but must estimate data for such consumers. Utilities will estimate base year and base billing period data for all major use consumers for whom no actual billing data exists.