Surveying
Which of the following errors can be eliminated by taking mean of bot face observations ?

error due to imperfect adjustment of plate levels
error due to eccentricity of verniers
error due to line of collimation not being perpendicular to horizontal axis
error due to imperfect graduations

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

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

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