At the National Institute of Metrology (NIM), China, the Small Angle Measuring System, which is based on the sine principle, was developed as the national primary standard for the plane angle in an angular measuring range of ±5°. The measurement uncertainty of this system is dominated by the accuracy of an invar angular interferometer optical system. To calibrate this angle interferometer system, a series of known reference standards were generated with a multi-step method using a double-deck rotary table. The measurement uncertainty of the calibration is estimated to be approximately 0.05’’ (k=2).

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