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The external-probe fog gloss meter is based on a laboratory instrument used in the paper industry during that era. Due to technological advancements and stricter aesthetic requirements, the deviation of the gloss unit (GU) has been significantly reduced. Some instrument manufacturers claim that their gloss meters can achieve accuracy of 0.1 GU, while application specifications often specify a range of 1 GU as the acceptance standard. The gloss reference points defined in the standard are the 0GU and 100GU reference standards. The 0GU reference standard is a completely light-free surface with zero reflection. The reference standard for 100GU is based on black or quartz glass. Refractive index is the angle change that occurs when light passes from one medium to another at a specific wavelength, and it is used to calculate the reflectivity of a surface. The calculation can be completed by using the Fresnel equation. Fogging is a phenomenon unique to highly glossy surfaces. Therefore, using a 20° angle light path is similar to using a 20° gloss meter. The aperture range of the 20° gloss meter is 18°; two additional probes located next to the gloss probe measure the intensity of the diffused light that represents haze. In this way, the specularly reflected light and the scattered light are measured simultaneously. The shadow value is expressed in logarithmic form to better align with visual observations; the lower the shadow reading, the better the surface quality. Shenzhen Huafeng Technology Co., Ltd. explains how to use the external probe haze and gloss meter: 1. Degree of dispersion: The effect of the degree of dispersion on gloss and haze. When the gloss values are nearly the same, pigment particles smaller than 10 μm can significantly reduce haze. 2. Coating types: In practical applications, it is very important to test the coordination of the coating process flow. Different coating systems were coated using electrostatic and pneumatic devices respectively: The system formed flocculation under electrostatic spray gun conditions, resulting in an increased haze value. The system shows that pneumatic spraying yields a good low fog shadow value, while electrostatic spraying tends to cause flocculation. The system is quite suitable for both spraying methods. 3. Polishing: Other causes of hazy shadows include weathering and polishing marks. Measuring both gloss and haze simultaneously helps to objectively evaluate surface quality. The enhanced version of the portable instrument, the micro mist shadow meter, and the desktop instrument, the mist shadow gloss meter, specifically designed for laboratories.