Experiment on Accuracy of Optical Theodolites

Five optical theodolites of different designs and least counts are compared for accuracy in reading horizontal angles. A subtense bar of an accurately known length and a Wild T3 precision theodolite are used for this purpose. Subtended angles are first measured using the Wild T3. These are then remeasured using each of the test instruments. The root‐mean‐square‐error values of angle measurement are then computed as standard deviations. The best accuracy values are obtained with the double‐reading micrometer theodolites. However, in almost all cases considered, the optical scale‐reading theodolites give accuracy values approximating those obtained with a single‐reading micrometer type of instrument.