GB/T 9754-2025 "Paints and varnishes - Determination of specular gloss at 20°, 60° and 85°" specifies methods for measuring the gloss of coatings under three geometric conditions, applicable to non-textured coatings on smooth, opaque substrates. Gloss values are expressed in gloss units (GU), calculated as the ratio of the luminous flux reflected from the sample to that from a reference black glass. The 60° angle is the general measurement angle, 20° is suitable for high-gloss coatings with 60° measurement values >70 GU, and 85° is suitable for matte coatings with 60° measurement values <10 GU. The standard clarifies the optical structure requirements for glossmeters, which must be calibrated using high-gloss, medium-gloss, zero standard plates, and certified reference materials. During measurement, at least five representative positions should be selected and averaged. It also includes analysis of error sources and requirements for laboratory environmental control.