ISO 4259 Petroleum products - Determination and application of precision data in relation to methods of test
9 Quality control against specifications
9.1 General
Clause 9 provides general information to allow the supplier or the recipient to judge the quality of a product with regard to the specification when a single result is available. If it is necessary for the recipient to take action after examining this result, the procedure specified in Clause 10 shall be adopted.
9.2 Testing margin at the supplier
A supplier who has no other source of information on the true value of a characteristic than a single result shall consider that the product meets the specification limit, with 95 % confidence, only if the result, X, is such that
- in the case of a single upper limit, A1: X ≤ A1 − 0.59R (27)
- in the case of a single lower limit, A2: X ≥ A2 + 0.59R (28)
- in the case of a double limit (A1 and A2), both these conditions are satisfied (see 7.2.3).
The use of Equations (27) and (28) is for the guidance of the supplier and is not to be interpreted as an obligation. A reported value between the specification value and the limit from Equation (27) or (28) is not proof of non-compliance.
9.3 Testing margin at the recipient
A recipient who has no other source of information on the true value of a characteristic than a single result shall consider that the product fails the specification limit, with 95 % confidence, only if the result, X, is such that:
- in the case of a single upper limit A1, X > A1 + 0.59R (29)
- in the case of a single lower limit A2, X < A2 − 0.59R (30)
- in the case of a double limit (A1 and A2), either of these conditions applies.
