Golden sample
also: golden unit · reference sample · master sample
A unit formally approved as the reference for how the product must look, feel and perform; production units are compared against it.
Some attributes are hard to capture fully in drawings: color, gloss, texture, button feel, gap uniformity, sound. A golden sample signed off by both the brand owner and the factory settles disputes, because production units must match it within agreed limits. Separate golden samples may exist for subassemblies, packaging and printed materials, and "golden units" are also used to check that test stations are measuring correctly.
Golden samples age (colors fade, materials creep), so store them carefully, and replace and re-sign them after every approved design change.
Founder takeaway
Sign and store golden samples, with matching sets held by you and the factory, for anything cosmetic or subjective, and update them after each approved change.
engineer review pending