Abstract:Starting from the establishment of the formula system for calculating plumb line deviation, the relation and conversion process among the numerical scale index s, the Angle θ between plumb line and gravity line, the plumb line deviation ΔL of the plumb instruments at a certain altitude are demonstrated by examples.The cumulative error of the optical (laser) plummet is analyzed by focusing on the connection between the zenith and nadir plumb line. Focusing on the correlation between pentagonal prism and biplanar mirror system, the negative influence of pentagonal prism on plumb line deviation is calculated. The calibration devices of the plumb instruments are divided into two types and the errors of counting principle which they embody are analyzed in a popular way. Finally, the comparative advantage of the accuracy of the plumb instruments is explained through the comparison with the laser marker.