Going back further in time, one can examine the cancellation patterns of CBS for their Friday night shows.
Over the last decade or so, most of CBS's single season and multi-season Friday evening shows were canceled when the viewer numbers were in the 7 million range (or less). For example, shows like:
2002-2003: Robbery Homicide Division
2009-2010: Ghost Whisperer, Numb3rs, Miami Medical
2010-2011: Medium, CHAOS
Several CBS Friday night shows were canceled with higher viewer numbers than 7 million, such as: Joan of Arcadia (8 million), JAG (9-10 million), Close to Home (10 million).