Significance and Use
4.1 This practice provides a means whereby the parties to a transaction can resolve potential quality disputes over those product properties which can be tested and expressed numerically.
4.1.1 This practice can be used to ensure that such properties are correctly stated on labels or in other descriptions of the product.
4.1.2 This practice can be implemented in those cases where a supplier uses an in-house or a commercial testing laboratory to sample and test a product prior to releasing the product to a shipper (intermediate receiver) and the ultimate receiver also uses an in-house or commercial testing laboratory to sample and test the product upon arrival at the destination. The ATV would still be determined according to 8.3.
4.2 This practice can assist in the determination of tolerances from specification limits which will ensure that the true value of a property is sufficiently close to the specification value with a mutually agreed probability so that the product is acceptable to the receiver. Such tolerances are bounded by an acceptance limit (AL). If the ATV value determined by applying this practice falls on the AL or on the acceptable side of the AL, the product can be accepted; otherwise it shall be deemed to have failed the product acceptance requirement established by applying this practice.
4.3 Application of this practice requires the AL be determined prior to actual commencement of testing. Therefore, the degree of criticality of the specification, as determined by the Probability of Acceptance (P value) that is required to calculate the AL, shall have been mutually agreed upon between both parties prior to execution of actual product testing.
4.3.1 This agreement should include a decision as to whether the ATV is to be determined by the absolute or rounding-off method of Practice E29, as therein defined.
4.3.1.1 If the rounding-off method is to be used, the number of significant digits to be retained must also be agreed upon.
4.3.1.2 These decisions must also be made in the case where only one party is involved, as in the case of a label.
4.3.1.3 In the absence of such an agreement, this practice recommends the ATV be rounded in accordance with the rounding-off method in Practice E29 to the number of significant digits that are specified in the governing specification.
4.4 This practice is designed to be suitable for reference in contracts governing the transfer of petroleum products and lubricants from a supplier to a receiver.
4.5 As a prerequisite for acceptance for lab test results to be used in this practice, the following conditions shall be satisfied:
4.5.1 Site precision (R′) as defined in Practice D6299 for the appropriate test method(s) from each lab, as substantiated by in-house quality control programs, for property typical of the product in dispute, should have a TPI > 1.2 (see Practice D6792 for TPI explanation), but at a minimum shall be better than the published method reproducibility (R).
4.5.2 Each lab shall be able to demonstrate, by way of results from interlaboratory exchange programs, a lack of a systemic bias relative to exchange averages for the appropriate test method(s) as per methodology outlined in Guide D7372.
4.5.3 In the event that the site precision of laboratories from two parties are statistically different as confirmed by the F-test (see Annex A4), then, for the purpose of establishing the ATV, each laboratory's test result shall be inversely weighted in accordance with laboratory's demonstrated variance.
4.6 It is recommended that this practice be conducted under the guidance of a qualified statistician.
Scope
1.1 This practice covers guidelines and statistical methodologies with which two parties, usually a supplier and a receiver, can compare and combine independently obtained test results to obtain an Assigned Test Value (ATV) for the purpose of resolving a product quality dispute.
1.2 This practice defines a technique for comparing an ATV with a specification limit.
1.3 This practice applies only to those test methods which specifically state that the repeatability and reproducibility values conform to the definitions herein.
1.4 The statistical principles and methodology outlined in this practice can also be used to obtain an ATV for specification conformance decision when multiple results are obtained for the same batch of product within a single laboratory. For this application, site precision (R') as defined in Practice D6299 shall be used in lieu of test method published reproducibility (R).
