1. The work surface should be free of rust, scratches, dents, and other cosmetic defects that may affect use.

2. Work surfaces should not have casting defects such as sand holes, blow holes, cracks, inclusions, and shrinkage. All casting surfaces should be free of molding sand, with smooth and even surfaces, and paint should be firmly applied. All sharp edges should be rounded off. On flat work surfaces with precision levels lower than "00," sand holes with diameters less than 15mm may be filled with the same material, but the hardness should be lower than that of the surrounding material. The filled areas on the work surface should not exceed four, and the distance between them should be no less than 80mm.

3. On the two side surfaces, threaded holes or cylindrical holes for hoisting devices such as handles and rings should be installed. When designing the hoisting position, consider minimizing the changes caused by the hoisting process.

4. Upon customer request, threaded holes or grooves should be set on the board work surface, but no protrusions higher than the work surface should appear in these areas.

5. Fine-grained gray cast iron or alloy cast iron should be used for manufacturing.

6. The hardness of the working surface should be HB170-220.

7. The working surface should employ a scraping process. For "3" grade flat working surfaces, planing process can also be used. The surface roughness of the planed working surface, calculated as the arithmetic mean deviation Ra, should not exceed 5 μm.

8. The products should be treated for stability and degaussed. Flatness: It can be divided into three levels - Laboratory Grade (Reference), Calibration Grade (Master), and Workshop Grade (Working).

AA Grade: Its flatness (μm) = 1 + 1.6D² (D being the diagonal length or diameter of the platform), used for highly precise measurements, commonly used in laboratories.

②.A Grade: Twice the accuracy of AA-grade flatness, commonly used in tool inspection rooms for the calibration of precision measuring tools.

③.B Grade: Four times the error of the AA grade in flatness, commonly used for tool inspection rooms or on-site inspection of gauges or marking lines.

Surface Grinding: In the early days, people used three platforms to match each other to create a true flat plane. A skilled and patient stone dresser could produce an astonishingly flat surface without any measuring instruments, simply by rotating the platforms through 90 degrees multiple times.