Surveying
The scale of a tilted photograph of focal length f, taken from an altitude H, along the plate parallel through plumb point, is

f sec θ/H
f/H cos ½θ
f/H sec θ
f/H

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

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

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