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After the line is drawn, you should determine the maximum deviation of the deviations of the surface of the ceiling from this line. In the event that the deviation of the surface of the ceiling from the specified level is less than 50 millimeters, then the surface of the ceiling can be aligned with special dry mixtures. In the event that the deviation is more than 50 millimeters, other mixtures should be used. It is necessary to consult with experts about the choice of materials.