How to check the flatness error of granite platforms?

The quality, accuracy, stability, and longevity of the raw materials used to produce granite platforms are crucial. Extracted from underground rock layers, they have undergone hundreds of millions of years of natural aging, resulting in a stable shape and no risk of deformation due to typical temperature fluctuations. Marble platforms undergo rigorous physical testing, and the materials used are selected for their fine crystals and hard texture. Because marble is a non-metallic material, it exhibits no magnetic reactivity and exhibits no plastic deformation. So, do you know how to test the flatness error of granite platforms?
1. Three-point method. A plane formed by three distant points on the actual surface of the marble platform being tested is used as the evaluation reference plane. The distance between two planes parallel to this reference plane and with a small distance between them is used as the flatness error value.
2. Diagonal method. Using one diagonal line on the actual measured surface of the marble platform as the reference, a diagonal line parallel to the other diagonal line is used as the evaluation reference plane. The distance between two planes containing this parallel plane and with a small distance between them is used as the flatness error value.

3. Multiplying two test methods. The least squares plane of the actual measured marble platform surface is used as the evaluation reference plane, and the distance between two enclosing planes parallel to the least squares plane and with the smallest distance between them is used as the flatness error value. The least squares plane is the plane where the sum of the squares of the distances between each point on the actual measured surface and that plane is minimized. This method is computationally complex and typically requires computer processing.
4. Area Detection Method: The width of a small enclosing area, including the actual measured surface, is used as the flatness error value. This evaluation method meets the definition of granite platform flatness error.