Abstract: A method for determining and correcting positional errors or deviations which occur when measuring the position of a point in space, or when positioning to a point which has a specific position in space, where the position refers to a specific coordinate system, such as a rectangular coordinate system. The method comprises making a comparison between a multiple of measured values and at least one reference, and determining a correction on the basis of this comparison, wherewith a positionable member, such as a contact probe, a tool holder or corresponding device (1, 13) is moved to a given position in space during the measuring or positioning process. The method is particularly characterized in that the reference consists of a geometry of known kind, and in that the measured values are correlated to a geometry of known kind, this correlation being used to calculate corrections for the coordinate axes of the system. There is also an apparatus for carrying out the method.