A computer-implemented medical method of automatically determining an orientation of a medical instrument base (206, 303) in relation to a robotic system (200, 300), the method excluding any method of surgery excluded from patentability according to Article 53 (c) EPC, the method comprising the following steps: - acquiring first movement data associated with a movement of the robotic system relative to a first reference; wherein the step of acquiring first movement data comprises recording at least an initial position and a final position of the robotic system, - acquiring second movement data associated with a movement of a marker device relative to a second reference, wherein the step of acquiring second movement data comprises recording at least an initial position and a final position of the marker device, - wherein the marker device is attached to the medical instrument base, - wherein the medical instrument base is movably attached to the robotic system, the method further comprising the steps - determining a relative movement of the robotic system from its initial to its final position, - determining a relative movement of the medical instrument base from its initial to its final position, - comparing the first and second movement data and determining a comparison result, wherein the step of comparing the first and second movement data comprises comparing the relative movement of the robotic system with the relative movement of the medical instrument base, and - using the comparison result for determining the orientation of the medical instrument base in relation to the robotic system,and - wherein the acquisition of the first movement data associated with the movement of the robotic system is not based on tracking a marker positioned at a housing of the robotic system. - acquiring first movement data associated with a movement of the robotic system relative to a first reference; wherein the step of acquiring first movement data comprises recording at least an initial position and a final position of the robotic system, - acquiring second movement data associated with a movement of a marker device relative to a second reference, wherein the step of acquiring second movement data comprises recording at least an initial position and a final position of the marker device, - wherein the marker device is attached to the medical instrument base, - wherein the medical instrument base is movably attached to the robotic system, the method further comprising the steps - determining a relative movement of the robotic system from its initial to its final position, - determining a relative movement of the medical instrument base from its initial to its final position, - comparing the first and second movement data and determining a comparison result, wherein the step of comparing the first and second movement data comprises comparing the relative movement of the robotic system with the relative movement of the medical instrument base, and - using the comparison result for determining the orientation of the medical instrument base in relation to the robotic system,and - wherein the acquisition of the first movement data associated with the movement of the robotic system is not based on tracking a marker positioned at a housing of the robotic system.