The circular level is installed on the base of the level for rough leveling. It is a sealed glass round box with a circular bubble inside. The inner surface of the glass on the top surface of the circular level is ground into a spherical surface. The center of the spherical surface is engraved with a circle, and its center is called the zero point of the circular level. The spherical normal L'L' of the zero crossing point is called the axis of the circular hydroscope. The circular level axis L'L' is parallel to the vertical axis VV of the instrument. As shown in Figure 2-8. When the center of the bubble deviates from the zero point by 2mm, the angle value of the vertical axis is called the division value of the circular level, which is generally 8'-10', and the accuracy is low.