This Report provides guidance for the parties to the test to establish the degree of uncertainty of the test results when there are deviations from requirements of PTC 6 (The Code). This Report does not contain a complete test procedure. It should be used only in conjunction with the Code. Compliance with the Code is expected where no alternative is shown in this Report. Numerical values have been assigned to the uncertainty of instruments of various qualities. These numerical values, representing the consensus of knowledgeable professional people, cover 95% uncertainty intervals and therefore will be exceeded, on average, in one instance in 20.