Orientation Error of the LLMC and its Detection

The source of the orientation error of the LLMC is analyzed in this paper. The necessity to set an azimuth detection system is discussed, and parameters of the system are also presented. The precision of the ball-locating disk is estimated. The modified precision of the LLMC can not be obtained if we only rely on improving the instrumental stability and the manufacturing accuracy. The open questions in the detection system and the improvement are described in the paper.