Bubble level, also known as a spirit level, determines the horizontal state of the surface by the relative position of the internal liquid and bubbles. It mainly consists of a small tube filled with liquid, with a small bubble inside, and transparent disks at both ends engraved with reference scales. By gravity, the bubble is kept in a horizontal position. When the level is tilted, the bubble in the level tube will move towards the rising end, indicating the direction and degree of tilt. The curvature radius of the inner wall of the leveling tube determines the accuracy of the level, and the larger the curvature radius, the higher the resolution.