Surveying
The distance between the minor control point and the principal point should be equal to

Sum of the base lines of stereo pair
Mean of the base lines of the stereo pair
Base line of the right photograph of stereo pair
Base line of the left photograph of stereo pair

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Surveying
The error due to eccentricity of inner and outer axes can be eliminated by

double sighting
reading both verniers and taking the mean of the two
taking both face observations and taking the mean of the two
taking mean of several readings distributed over different portions of the graduated circle

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