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We present the design, setup and preliminary results for a navigation system based on magnetic field sensors. Our system localizes the tip of a magnetized steel rod with diameter 0.5 mm in a cubic workspace with 30 mm edge length. We plan to localize electrodes and probes during surgeries, e.g. for small animal research like neurosurgery in rats. Only the static magnetic field of the steel rod is needed for localization. Our navigation system does not need any external excitation, wires or alternating magnetic fields. Hence, we avoid undesirable stimulation of the animal's brain and we are able to realize small (0.5 mm) probe diameters to reduce brain damage. Localization of the steel rod's tip is achieved using a nearest neighbor approach. The currently measured sensor values are compared to data stored in a previously generated lookup table. An industrial robot is used to create the lookup table and later to validate the accuracy of the system. Currently, the system has 3 degrees of freedom (DOF). Mean of the difference between true and determined position is -0.53; 0.31; -0.95 [mm] with a standard deviation of 1.13; 1.24; 0.99 [mm] in XYZ, or lower. The influence of different noise sources, e.g. electric currents or metal, on the performance of the system are discussed.