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Various dynamic goniometric systems are applied in modern practice to measure a plane angle in dynamics with high accuracy. As a rule, these systems are either designed to measure the angles of optical prisms, or they are verified/calibrated using optical polygons, that are standard angular measures. Optical null-indicators of various types are used in dynamics to bind the reflecting faces of the prism to the measuring system. Until recently the interference null-indicator could be regarded to provide the best measurement accuracy, but it has one significant drawback. This type of null-indicator is highly sensitive to the propagating wavefront quality and thus it cannot be used other than at short distances and in stable environment. For several years, the authors have been developing and researching various modifications of null-indicators based on the autocollimation principle, which are more robust considering the operating conditions. Preliminary tests of prototypes have shown that such devices are also capable of providing accuracy of angular measurements at the level of hundredths fractions of an arc second, as well as interference ones. It is known that quality of the reflecting surface may affect the high precision angle measurements conducted by optical non-contact means. When comparing the measurements involving null-indicators that implement different optical principles, this influence may become even more significant. The paper presents the experimental comparison research of interference and autocollimating null-indicator performance. Both null-indicators were installed simultaneously as a components of high precision laser dynamic goniometer. The 8- sided optical polygon with known flatness parameters of reflecting faces was used as a test object. In order to distinguish the measurement error determined by the reflecting surface flatness and null-indicator type from the total measurement error the cross-calibration procedure was carried out.
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