A measurement campaign was carried out at the Geodetic Observatory Wettzell in order to determine the reference point of a radio telescope used for Very Long Baseline Interferometry (VLBI) at better than 1 mm. This point has been determined by measuring the trajectories of targets installed on the telescope, using two commercial total stations, but also a prototype of multilateration system composed of one absolute distance meter and of four measurement heads. The use of prototypes is always subject to risk, so the produced data must be carefully checked. This paper evaluates independently the data from the multilateration system to ensure that they are compatible with the intended purpose. Despite the unstable position of one of the measurement heads, position uncertainties between 46 μm and 304 μm were assessed for the targets installed on the radio telescope, depending on uncertainties of the distance measurements, target visibility, and the positions of the targets relatively to the heads. These results validate the use of the multilateration system, even if the position measurements of some survey pillars of the local site network have shown larger uncertainties, of several hundred of micrometres. At the end, the measurements of the multilateration system have been combined with those of the total stations, a global network adjustment was performed, and the coordinates of the VLBI reference point were determined with related standard deviations of 0.06 mm, 0.04 mm, and 0.10 mm for the x, y, and z axes, respectively.