More than three dilution may remain after removal of the lowest dilution with all positive tubes and high dilutions will all negative tubes. In this case, if the highest dilution with all positive tubes is within two dilutions of the highest dilution with any positive tubes, than use the highest dilution with any positive tubes and the two immediately lower dilutions. In example C, the highest dilution with all positive tubes is 0.1 ml, which is within two dilutions of 0.001 ml, which has one positive tube. In example D, the highest dilution with all positive tubes is 0.01 ml, which is within two decimal dilutions of 0.001 ml, to yield a combination of 4-5-1.