A tracker device (10,10,10") of the type associated with a surgicalinstrument and being trackable in space by a CAS system (100) such that aposition of the surgical instrument is calculable. A support (12) is adaptedto be connected to the surgical instrument. Optical elements are mounted tothe support (12) in a first pattern (44A) so as to be detectable by the CASsystem along a first range of visibility. Other optical elements are mountedto the support in a second pattern (44B,44C) so as to be detectable by the CASsystem along a second range of visibility, with the first range of visibilityand the second range of visibility having at most a common portion, whereby aposition of the surgical instrument is tracked within the first and the secondrange of visibility as a function of the detection of any one of the patterns(44A,44B,44C) of the optical elements.
