The invention relates to a data processing method for identifying a medical instrument (5) which is configured to be tracked by means of a medical tracking system (4), wherein the method is designed to be executed by a computer and comprises the following steps:—acquiring relative position and/or movement data which comprise relative position and/or movement information describing a relative position and/or movement between a calibration tool (1), which comprises at least one supporting surface (2), and the medical instrument (5) which is in contact with the side or edge of the at least one supporting surface (2), respectively;—acquiring geometry data which comprise geometry information describing at least one geometrical feature for a plurality of candidate instruments;—determining, on the basis of the relative position and/or movement data and the geometry data, candidate data which comprise candidate information describing at least one candidate instrument from the plurality of candidate instruments, the at least one geometrical feature of which would allow the relative position and/or movement between the medical instrument (5) and the calibration tool (1).