ISO 4259 test precision
Repeatability, reproducibility and the interpretation rule that decides most bunker quality disputes when a result sits marginally outside a specification limit.
ISO 4259 is the standard that governs how the precision of a petroleum test method is determined and, more importantly for shipping, how a test result is compared against a specification limit. It is the reason a bunker sample can test marginally outside an ISO 8217 limit and still not sustain an off-specification claim, and it decides more quality disputes than any point of chemistry does.
The full article will set out the two precision statistics and what each means. Repeatability is the difference expected between two results on the same sample by the same operator with the same apparatus. Reproducibility is the larger difference expected between two laboratories testing the same sample. Both are stated for each test method, and both are needed before a single number can be called a failure.
The article will then work through the interpretation rule as it is actually applied to a bunker stem: how a result is compared with a limit, what a supplier and a buyer are each entitled to argue when their laboratories disagree, why a second test at a third laboratory is often the practical resolution, and how supply terms and charter party bunker clauses incorporate the standard. It links to ISO 8217:2024 and marine gas oil .