Used primarily in the calibration and standardization of color measurement instruments, especially for determining the yellowness or color intensity of water and chemicals. Commonly applied in water quality testing to match the appearance of samples against standardized platinum-cobalt color units (Hazen units). Ensures consistency in industries such as pharmaceuticals, beverages, and wastewater treatment where visual clarity and color are critical quality parameters. Also used in laboratories for creating colorimetric reference scales and validating spectrophotometer performance.