Abstract: An apparatus for monitoring the spatial position of a reference point relative to a predetermined origin, the reference point being located on an articulated marine loading arm having a plurality of pivotally interconnected fluid conduits forming pivot angles at the interconnections of the conduits, includes segments subtended by the pivot angles and means are provided for sensing lengths of the segments as the loading arm articulates. The sensing means generate electrical signals proportional to the segment lengths and a computer receives the electrical signals and calculates the position of the reference point therefrom based on the known geometry of the loading arm.