Excerpt from the original CRV manual by Paul H. Smith:

“Mobility”, the second movement concept, is the ability possessed by the viewer in Stage III to shift his viewpoint to some extent from point to point about the site, and from one perspective to another, i.e., further back, closer up, from above, or below, etc. This ability makes possible the production of trackers and sketches as described below. An additional feature this introduces is the ability to shift focus of awareness from one site to another using a polar coordinate concept.