The high-accuracy automatic refratometer for wide spectrum is based on the method of vertical incidence and symmentrical refraction. Closed measurement of the three angles of the triple prism was carried on to improve the test accuracy. This paper analyzes the errors produced by the light beam collimateion

the verticality between the collimated beam and the base side of thprism

the angle defference

the angle measuring accuracy and the aiming accuracy

etc. The measured deviation of the index is less than 3?10

-6

in visible and infrared spectrum. It shows

by comparision with the method of minimum deviation by the tested data

that the two methods have the same accuracy.