Reference standard
Reference standard turns up in 2 fields: paper optics, metrology. Here is what it means to the people in each one.
Reference standard in paper optics
Certified material with assigned reflectance values that transfers a measurement scale to a working instrument.
Paper labs calibrate against standards traceable to the perfect reflecting diffuser: opal glass, ceramic or pressed-powder references for the white scale, and fluorescent paper standards for UV adjustment. The values come from an authorized laboratory and carry an expiry, because paper and fluorescent standards age. An out-of-date standard shifts every brightness and whiteness value the lab reports by the same error.
"New IR3 reference standards came in, so retire the old set and log the switch in the instrument book."
Reference standard in metrology
A lab's highest-level standard for a quantity, used only to calibrate other standards and never for routine work.
The best standard an organization holds for a quantity, reserved for calibrating its other standards and kept at the top of the lab's own hierarchy. It is calibrated externally, often by a national metrology institute or a higher-tier accredited lab, handled minimally and stored under controlled conditions to protect its stability. Using it for daily jobs wears it out and defeats its purpose, which is why working standards exist.
"Don't use the reference standard mass set on the shop scales, that's what the working set is for."