A computer-implemented medical data processing method for controlling the geometric status of a passive mechatronic articulable arm, the method comprising executing, on at least one processor of at least one computer, steps of: a) acquiring (S1.1), at the at least one processor, current device position data describing a current relative position between a utility element of the passive mechatronic articulable arm and an anatomical body part of a patient's body; b) acquiring (S1.2), at the at least one processor, current geometric status data describing a current geometric status of the passive mechatronic articulable arm defined by a set of at least one current spatial relationship between connected elements of the passive mechatronic articulable arm, wherein the number of connected elements is at least three; c) acquiring (S1.3), at the at least one processor, changed device position data describing a changed relative position between the utility element and the anatomical body part which is a relative position that has changed compared to the current relative position; d) acquiring (S1.4), at the at least one processor, device definition data describing the movability of the passive mechatronic articulable arm; e) determining (S1.5), by the at least one processor and based on the current device position data and the current geometric status data and the changed device position data and the device definition data, changed geometric status data describing a changed geometric status of the passive mechatronic articulable arm defined by a set of at least one changed spatial relationship between the connected elements, wherein the set of at least one changed geometric relationship is different from the set of at least one current spatial relationship; f) determining (S1.6), by the at least one processor and based on the current geometric status data and the changed geometric status data, instruction data describing an instruction for manually changing the geometric status of the passive mechatronic articulable arm from the current geometric status to the changed geometric status, wherein the set of at least one changed spatial relationship between the connected elements comprises only a minimum number of spatial relationships changed to achieve the changed geometric status, wherein that the instruction data describes an instruction for changing only the respective at least one current spatial relationship to the respective at least one changed spatial relationship, and wherein the instruction is output to a user by using a visual output device or an acoustic output device or a tactile output device. a) acquiring (S1.1), at the at least one processor, current device position data describing a current relative position between a utility element of the passive mechatronic articulable arm and an anatomical body part of a patient's body; b) acquiring (S1.2), at the at least one processor, current geometric status data describing a current geometric status of the passive mechatronic articulable arm defined by a set of at least one current spatial relationship between connected elements of the passive mechatronic articulable arm, wherein the number of connected elements is at least three; c) acquiring (S1.3), at the at least one processor, changed device position data describing a changed relative position between the utility element and the anatomical body part which is a relative position that has changed compared to the current relative position; d) acquiring (S1.4), at the at least one processor, device definition data describing the movability of the passive mechatronic articulable arm; e) determining (S1.5), by the at least one processor and based on the current device position data and the current geometric status data and the changed device position data and the device definition data, changed geometric status data describing a changed geometric status of the passive mechatronic articulable arm defined by a set of at least one changed spatial relationship between the connected elements, wherein the set of at least one changed geometric relationship is different from the set of at least one current spatial relationship; f) determining (S1.6), by the at least one processor and based on the current geometric status data and the changed geometric status data, instruction data describing an instruction for manually changing the geometric status of the passive mechatronic articulable arm from the current geometric status to the changed geometric status, wherein the set of at least one changed spatial relationship between the connected elements comprises only a minimum number of spatial relationships changed to achieve the changed geometric status, wherein that the instruction data describes an instruction for changing only the respective at least one current spatial relationship to the respective at least one changed spatial relationship, and wherein the instruction is output to a user by using a visual output device or an acoustic output device or a tactile output device.