光电经纬仪测量元素误差是外弹道测量中最主要的误差源。为了保证外弹道的测量精度，就应对光电经纬仪的测量精度进行合理设计。通过数学解析的方法，推导建立了2个简洁的公式：1)单站定位体制下弹道点位精度和光电经纬仪测角、测距精度以及目标斜距、高角之间的数学表达式；2)对称交会测量体制下弹道点位精度和光电经纬仪测角精度以及目标斜距、交会角之间的数学表达式。这2个公式为光电经纬仪精度指标的设计论证提供了理论依据。

Measurement error from the photoelectric theodolite is the main error in the ballistic trajectory measurement. In order to measure ballistic trajectory accurately,the measurement precision of the photoelectric theodolite should be investigated. The measurement accuracy of the photoelectric theodolite is decided based on measurement requirement of the ballistic trajectory. Two simple equations were derived mathematically,one expression for positioning error of the ballistic trajectory,angle error of the photoelectric theodolite,ranging error,target slant range and height when one instrument is used,another expression for positioning error of the ballistic trajectory,angel error of the photoelectric theodolite,target slant range and intersection angle when two symmetrical intersection instruments are used. The two equations provide a theoretical base for designing precision of the photoelectric theodolite.