Surveying
To avoid large centering error with very short legs, observations are generally made

To a target fixed on theodolite tripod on which theodolite may be fitted easily
By using optical system for centering the theodolite
All listed here
To chain pins

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Surveying
Circumpolar stars

Remain always above the horizon
Are seldom seen near the pole star
Rotate round the North Pole
Rotate round the celestial pole

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