In-situ leveling calibration of surveying instrument

The invention relates to field leveling calibration of surveying instruments. A surveying instrument comprises: at least one rotational movement shaft for providing positioning of a measurement direction of the surveying instrument; a rotational position encoder configured to obtain a rotational direction value about the movement axis; and an acceleration sensor for obtaining leveling of the surveying instrument and rotatable about the rotational movement axis at different rotational positions. The instrument further comprises: a mechanism designed to move the acceleration sensor from the first orientation to at least one second orientation, the second orientation being different from the first orientation, where the mechanism is designed and arranged such that the aiming direction is not affected by the movement of the acceleration sensor by the mechanism; and an evaluation unit configured to derive a calibration leveling of the instrument based on position encoder readings in at least first and second diffe