Concept

Certificate SD fields

A CRM certificate carries several dispersion numbers, and they are not interchangeable. An OREAS certificate has a Table 1 (Certified Value | 1SD | 95% Confidence | 95% Tolerance) and separate Performance Gates (1SD | 2SD | 3SD | …). Two of those are explicitly disqualified from QC use, in the certificate's own words:

"95% Confidence Limits should not be used as control limits for laboratory performance." — "tolerance limits pertain to the homogeneity of the CRM only and should not be used as control limits."

The 1SD is the correct control-limit field. Confidence intervals and expanded uncertainty shrink as more labs certify the CRM — so using them gives a better-characterised CRM tighter false gates. The error is silent and always in the failing direction.

Vendor traps to know by name

  • OREAS (Feb 2026 onward): Table 1 dropped 1SD for 95% Expanded Uncertainty (half-width ≈ 1×SD). Read it as 2SD and every gate is ~2× too tight.
  • CDN (current): the column titled "Two Standard Deviations" contains 1SD (verified arithmetically). Older single-line CDN certs genuinely are 2SD. Same vendor, opposite conventions.
  • Rocklabs: sanctions no certificate field as a control limit at all — build limits from your own lab's data.
  • AMIS: the headline ± is the control-chart SD, not the between-lab SD.

And two structural traps: certified values are per-method (OREAS 254c certifies Au four different ways — analyte alone is not a unique key), and IND/nr must be parsed per-cell — a row can have a valid SD next to an IND tolerance.

In geoDB

geoDB stores certified values per method — the QC engine matches a standard's certified value to the analytical method on the certificate, which is exactly the discipline the per-method trap requires. Standards imported from the built-in OREAS/CDN library carry vetted 1SD values. When you enter a standard by hand from a certificate PDF, this topic is the checklist: find the true 1SD, not the headline ±.