The tracking device, which we were talking about earlier, consists of six degrees of measurement or six degrees of freedom, for example head location and orientation. So the head is straight to the side exactly what the image is to display, or it also lets you track objects, so that you can do a registration between virtual or real images. And similarly other hands or other body parts can also be tracked. And these trackers can be of different kinds, mechanical, magnetic, acoustic, optical, based upon what technology is used to track these things.

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