Patent ID: 7441340

Claim:
A method of operating a surveying instrument placed in a orthogonal XYZ-system at (0,0,0) having a movable unit, said instrument defining a sight line that is controllably rotatable around a first axis, essentially horizontal, and around a second axis, essentially vertical, wherein said second axis may be inaccurately positioned so that it deviates from a true vertical axis, and said first axis may deviate from being orthogonal to the second axis; the method comprising the steps of determining at least one of the following group of errors relating to the instrument and/or its location: a) a trunnion axis error T as a function of the deviation from 90 degrees between the first axis and the second axis; b) a horizontal collimation error C H , being the deviation between the sight line and the perpendicular angle as related to the first axis; and c) a total plumb error defined by components, P I and P II , being two separate angular values defining the tilt of the instrument as related to the plumb line through the same; and d) using these determined values in continuously controlling the alignment when aiming the instrument.