  We characterize the performance of a system based on a magnetoresistor array.
This instrument is developed to map the magnetic field, and to track a dipolar
magnetic source in the presence of a static homogeneous field. The position and
orientation of the magnetic source with respect to the sensor frame is
retrieved together with the orientation of the frame with respect to the
environmental field. A nonlinear best-fit procedure is used, and its precision,
time performance, and reliability are analyzed. This analysis is performed in
view of the practical application for which the system is designed that is an
eye-tracking diagnostics and rehabilitative tool for medical purposes, which
require high speed ($\ge 100$~Sa/s) and sub-millimetric spatial resolution. A
throughout investigation on the results makes it possible to list several
observations, suggestions, and hints, which will be useful in the design of
similar setups.
