A method of determining a target spatial coordinate using an apparatus comprising a movable hand-held probe, having a body and a pointing element for pointing said target spatial coordinate, and a portable base unit provided with line-of-sight distance coupling means, wherein said hand-held probe is coupled to said portable base unit by said line-of-sight distance coupling means, coupled to said body at an attachment point, and wherein said base unit is provided with sensors providing measuring signals for measuring length or a change in length of said line-of-sight distance coupling means and angular direction of said line-of-sight distance coupling means in at least one degree of freedom, wherein said measuring signals correspond to spatial coordinates of said attachment point, and computer-controlled processing means communicatively connected to said sensors for processing measuring signals delivered by said sensors, the method further comprising the steps of: - retrieving, by said computer-controlled processing means, measuring signals from said sensors when said target spatial coordinate is appointed by said pointing element from different orientations of said hand-held probe, - determining, by said computer-controlled processing means, said target spatial coordinate from said measuring signals at each orientation of said hand-held probe, by one of: 1) determining said coordinates of said attachment point, determining virtual spheres having centres corresponding to said spatial coordinates of each attachment point, wherein radii of said spheres equal a crow flying distance between said attachment point and a pointing tip of said pointing element, determining an intersection point of said spheres, said intersection point being said target spatial coordinate, and: 2) determining said coordinates of each attachment point, determining one virtual sphere spanned by said coordinates of each attachment point, determining a centre of said sphere, said centre being said target spatial coordinate. - retrieving, by said computer-controlled processing means, measuring signals from said sensors when said target spatial coordinate is appointed by said pointing element from different orientations of said hand-held probe, - determining, by said computer-controlled processing means, said target spatial coordinate from said measuring signals at each orientation of said hand-held probe, by one of: 1) determining said coordinates of said attachment point, determining virtual spheres having centres corresponding to said spatial coordinates of each attachment point, wherein radii of said spheres equal a crow flying distance between said attachment point and a pointing tip of said pointing element, determining an intersection point of said spheres, said intersection point being said target spatial coordinate, and: 2) determining said coordinates of each attachment point, determining one virtual sphere spanned by said coordinates of each attachment point, determining a centre of said sphere, said centre being said target spatial coordinate. 1) determining said coordinates of said attachment point, determining virtual spheres having centres corresponding to said spatial coordinates of each attachment point, wherein radii of said spheres equal a crow flying distance between said attachment point and a pointing tip of said pointing element, determining an intersection point of said spheres, said intersection point being said target spatial coordinate, and: 2) determining said coordinates of each attachment point, determining one virtual sphere spanned by said coordinates of each attachment point, determining a centre of said sphere, said centre being said target spatial coordinate.