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Traditional roughness assessment is a two-dimensional parameter evaluation that is carried out along a single line, and it cannot fully reflect all the information of the entire surface; as a result, it increasingly fails to meet the needs of the manufacturing industry. The three-dimensional evaluation method for surface morphology utilizes the surface of a region to obtain the relevant information, providing insights into the mechanisms behind surface formation as well as intuitive images of the surface. This three-dimensional evaluation describes the surface characteristics of a part as a whole, thus offering a global perspective. There are many parameters for 3D surface roughness; today we will introduce the first one, Sa. Definition: Sa is the surface arithmetic mean height, which refers to the arithmetic or geometric average of the distances from the points on the contour surface to the central plane. In the sampling area D, it is the arithmetic average of the z-coordinate differences between the measured contour surface and the established reference plane; in other words, it is the arithmetic average of the absolute values of the z-coordinates in the surface roughness surface equation. The mathematical expression is as follows: Sa is commonly used to describe the surface roughness of precision-machined surfaces; it enables effective detection of the height characteristics across the entire area, thereby facilitating the formulation of machining processes. The Sa value varies significantly depending on the different processing methods. Evaluation of wafer surface roughness; the data were obtained using the SuperView W1 optical 3D surface profilometer from Zhongtu Instruments. History: In 2005, the latest draft standard ISO/TC213N756 issued by ISO/TC213 provided a detailed classification of parameters for the three-dimensional characterization of surfaces. These parameters were divided into 5 main categories – functional parameters, amplitude parameters, spatial parameters, comprehensive parameters, and volume parameters – totaling 23 parameters in all. Sa is one of the parameters included in the amplitude parameters category. On April 1, 2012, the International Organization for Standardization officially issued ISO 25178-2:2012 \"Geometric product specifications (GPS) – Surface texture: Regions – Part 2: Terms, definitions and surface texture parameters,\" which established the definition for Sa.