Concept

No certified SD

Sooner or later a standard has no usable certified SD — the whole certificate reports only expanded uncertainty, one analyte reads nr, or a row sits below detection (<5 IND IND — not a certified value at all; don't QC-evaluate it).

The sanctioned fallbacks, in order

  1. Derive the SD from your own lab's repeats. The unanimous vendor answer — OREAS: "SD's should be calculated directly from your own laboratory's process." AMIS wants a minimum of 20 analyses.
  2. OREAS's low-concentration rule: acceptance at Certified Value ±10% ±2DL — OREAS's published formula for near-detection grades (not CDN's; CDN certificates carry no such rule).
  3. The 5% window — a standing OREAS certificate column, calculated from the certified value.

⛔ Rules 2 and 3 produce acceptance WINDOWS, not standard deviations. Never enter a ±10%±2DL (or 5%) result in an SD field: the engine applies its 2SD/3SD ladder on top of whatever sits there, so a window entered as a 1SD silently widens your gates 2–3×. A window is the pass/fail test itself; only a real 1SD (rule 1 — your own lab's repeats) belongs in the SD field.

Explicitly not sanctioned: substituting the confidence interval, expanded uncertainty, or tolerance limits.

The trap with no support anywhere

Substituting the batch's own scatter — computing an SD from the very results you are judging — has no support in any source, and it is mechanically self-defeating: the calculated SD grows with the very error being detected. A uniformly wrong batch produces tight scatter → small Z → pass. This is not hypothetical; it has produced real massively-biased "Pass" verdicts in production databases (including, historically, this one — see below).

In geoDB

For most surfaces geoDB's ladder is: certified 1SD → an SD derived from the certificate's asymmetric 2SD bounds → a ±10%/±15% bias rule. On the certificate-detail page, however, a batch-scatter SD currently sits in the ladder for groups with no certified SD — a known, documented gap scheduled for remediation. So leaving the SD field blank is not a safe "bias-only" fallback: on the page that judges certificates, a blank SD means your standards get judged against the batch's own scatter — the very thing forbidden above. A hard bias ceiling (50% by default, configurable per project) backstops it: no row can "pass" with a huge bias no matter how the SD came out. If a standard of yours has no certified SD, the durable fix is to add a proper 1SD to the standard's record — from your lab's repeats, per the fallback ladder above.