The actual refinery production during the month of all fixed grades is compared with the production of the fixed grades in the combined or refinery DOP (Table 15 7). The differences between actual production and the DOP for fixed grades and process stocks are allocated to the participants as per a set of rules.

These differences, called deltas, between actual production and the combined DOP is allocated to the participants in such a way that the sum of two revised DOPs is made equal to actual production for all fixed grades and process stocks. This allocation of fixed-grade and process-stock deltas to the participants is called forecaster assigned changes or simply forecaster changes. Note that these changes are made only to fixed grades and process stocks and not to balancing grades. The objective is to revise the participants DOPs in such a way as to bring all fixed-grade production in the combined DOP equal to the actual production.