A tracker device of the type is associated with a surgical instrument and being trackable in space by a CAS system such that a position of the surgical instrument is calculable. A support is adapted to be connected to the surgical instrument. Optical elements are mounted to the support in a first pattern so as to be detectable by the CAS system along a first range of visibility. Other optical elements are mounted to the support in a second pattern so as to be detectable by the CAS system along a second range of visibility, with the first range of visibility and the second range of visibility having at most a common portion, whereby a position of the surgical instrument is tracked within the first and the second range of visibility as a function of the detection of any one of the patterns of the optical elements.