在In the measurement operation to eliminate or reduce all kinds of errors should be followed: (1) a measurement back must not change the focal length of the telescope (2) upper and lower half of the measurement between the vertical telescope, so that a measurement of the observation on the left side of the disk (3) on the second half of the measurement of the target In reverse order, and maintain that the operating time of each observation target is approximately the same (4) the bubbles of the standard unit in the observation shall not exceed the number of squares specified in the Code (5) the final operation of the micro-helix and micro-helix are "spin-in" and make