Surveying
For any star to be a circumpolar star, its

Hour angle must be 180°
Declination must be 0°
Declination must be 90°
Distance from the pole must be less than the latitude of the observer

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

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

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