Generally, there are three glass tubes in the level, and there is a bubble in each glass tube. Put the level bar on the object to be measured, which side of the bubble of the level ruler deviates to indicates that the side is on the high side, that is, it is necessary to lower the height of the side, or increase the height of the opposite side, and adjust the bubble to the center, which indicates that the measured object is horizontal in this direction. In principle, both horizontal and vertical are in the center, and the bubble with angle is naturally in the center. In general, the horizontal angle of the bubble is measured by measuring the horizontal angle of the water bubble. In addition, according to the principle of determining a plane by two intersecting lines, the level of the plane can be determined only by measuring two non parallel positions in the same plane