1, the principle of prism-free mode depends on laser reflection, and prism-free mode has a correction constant. After correction, the accuracy can still be guaranteed within 2cm, mainly because the position of the laser spot is determined, and the area where the laser beam hits the surface is a bit large, which is also one of the main reasons for the error. General construction lofting, you can use prism-free, convenient and fast.

2. Prism: Prism, a transparent object surrounded by two intersecting planes that are not parallel to each other, is used to split or disperse light beams. Prism is a polyhedron made of transparent materials (such as glass and crystal). It is widely used in optical instruments. Prisms can be divided into several types according to their properties and uses. For example, in spectral instruments, the "dispersion prism" that decomposes composite light into spectra is an equilateral prism; In periscope, binoculars and other instruments, right-angle prism is generally used to change the direction of light and adjust its imaging position.