DIN 55978 is a standard for the determination of relative Color-Strength in dyestuff solutions. The standard specifies the use of Spectrophotometric method, spectrophotometry to determine the relative Color-Strength of dyestuff solutions. The relative Color-Strength is calculated by comparing the Absorbance of the dyestuff solution to be tested with the reference dyestuff solution. This method is suitable for a variety of dyestuffs and can provide a scientific basis for the production, quality control and application development of dyestuffs. Through this standard, the chromadizing ability of dyestuff in solution can be accurately evaluated to ensure the performance conformity of the product in practical applications.