adjustment of plate levels

adjustment of line of sight

adjustment of horizontal axis

adjustment of altitude bubble and vertical index frame

levelling

prolonging a straight line

measurement of horizontal angles

all of the above

error due to eccentricity of verniers

error due to displacement of station signals

error due to wrong adjustment of line of collimation and trunnion axis

error due to inaccurate graduation

reading both verniers and taking the mean of the two

taking both face observations and taking the mean of the two

double sighting

taking mean of several readings distributed over different portions of the graduated circle

equal to true error

half the true error

two times the true error

four times the true error