If the three dilutions selected are not found in the table 9221:IV than something in the serial dilution was unusual. In this case, the usual methods for calculating the MPN, presented here, may not apply. If a new sample cannot be collected and an MPN value is still desired, use the highest dilution with at last one positive tube and the two dilution immediately lower as the three selected dilutions. In Example G, first selection, 4-3-6 (the outcome from the highest three dilutions), is not in table 9221:IV because 6 is greater than 5. The second selection. According to the above guidelines, would be 3-2-1. If this second set of selected dilutions is not in table 9221:IV, then use the following formula to calculate the MPN: