The invention relates to an inclination sensor for determining an inclination of an object with respect to a reference vector (75) of a reference coordinate system, comprising a tilt detector (18, 28) for determining gravity vector data of a local gravity vector (65), characterized by a position determination device (19, 29) for determining a position of the tilt detector (18, 28) and generating position data corresponding to the position of the tilt detector (18, 28), and a calculation unit (17, 27) comprising means for providing, based on the position data, position-related vertical deflection data, the vertical deflection data comprising information about a relation between the local gravity vector (65) and the reference vector (75), and calculation means (172) for calculating reference vector data based on the vertical deflection data and on the gravity vector data, wherein an inclination of the object with respect to the reference vector (75) is derivable from the reference vector data, to a surveying system comprising such an inclination sensor and to a method for determining the inclination of the object with respect to the reference vector (75).