So that the result of gluing is of high quality, and that the main thing is beautiful to carry out competent ceiling marking. This requires first to find its middle, using two threads that need to be pulled diagonally, their intersection and will be the middle of the ceiling. The marking does not end with this, after this, the determination of the middle of each of the walls and the drawing of the lines from this middle through the previously found center are required. Thus, four equal squares are obtained, which will become an excellent guideline during the installation of cassetons.