AX-R04 — Digit preference in declared purity

A chromatographic purity figure is the ratio of two integrated areas. It has no reason to land on a half or a whole percent, and across a large set of genuine measurements the terminal digit should be roughly uniform. It is not, on some certificates.

The rule requires a pattern rather than a single instance: a supplier must have at least three round-numbered declarations before any of them is flagged, because 99.0 % is a perfectly possible result once. Three times is a distribution.

Two explanations account for every instance the index has traced. The figure was rounded for presentation from a real integration — defensible, and recorded at full precision on the batch record even where the summary sheet carries the rounded form. Or the release specification was carried into the result field: "≥ 99.0 %" becoming "99.0 %" between the laboratory report and the summary sheet, which is the common case. In both, the underlying integration exists and is produced on request. Ask for the chromatogram rather than the summary and the rule resolves itself.

The rule cannot distinguish between the two from the certificate alone. What it can do is put the pattern next to the independent measurements of the same lots, and that comparison is the reassuring part: rounded declarations sit within half a point of the independent median about as often as unrounded ones do. This is a finding about how a number was written down, not about the material it describes, which is why the severity is low.