The Paper Dirt Tester is a specialized inspection instrument designed and manufactured in accordance with GB/T 1541-1989 (Paper and board — Determination of dirt). It is primarily used for the quantitative determination of surface dirt on various types of paper and paperboard. The instrument uses a 20W standard fluorescent lamp with a 60° irradiation angle to simulate standard illumination conditions, ensuring consistency and comparability of the observation environment. The worktable has an effective area of 0.0625 m² and can rotate 360°, facilitating comprehensive observation of large-area specimens from all directions. It is equipped with standard dirt comparison charts ranging from 0.05 to 5.0 mm, allowing quick visual determination of dirt grade by comparing fiber bundles and other impurities on the specimen surface with the standard charts. The overall dimensions are 750×350×500 mm with a weight of approximately 12.5 kg. The structure is robust and operation is intuitive. This instrument is a standard configuration device for paper surface quality inspection, cleanliness evaluation, and product grade assessment in paper mills, quality inspection agencies, packaging and printing plants, and research institutions.