There are several methods for specification inspection of Lu Grey stone.

Method 1: Measure using a steel straightedge with a graduation of 0.1MM. Place the straightedge on the two diagonals of the finished Luhei stone product, and use a feeler gauge to measure the gap between the straightedge and the board surface. The contract specifies that the maximum allowable tolerance for the floor plane is ±0.20MM.

Method Two: Measure the length, width, thickness, and diagonals using a standard steel ruler, and compare the measurements with the requirements specified in the contract. This is a commonly used method.

Method 3: Utilize an internal angle perpendicularity tolerance of 0.13MM, with internal angle side length of 450400mm steel square and feeler gauge measurements. Place the square's sides tightly against two edges of the sheet material, then use the feeler gauge to measure the gap between the sheet and the square's edges. Measure all four corners of the sheet using this method. The contract specifies an allowable tolerance of 0.40mm for angles. This method is used for the required stone products.