Sometimes it's compared with various real ranks like tennis' ATP.
ATP International Series | 2011 ATP Challenger Tour | 2012 ATP Challenger Tour | 2013 ATP Challenger Tour | ATP International Series Gold | ATP World Tour 250 series | ATP | ATP World Tour 250 Series | 2013 ATP World Tour | 2012 ATP World Tour | 2001 ATP Tour | 2011 ATP World Tour | ATP World Tour 500 series | 2010 ATP World Tour | 2003 ATP Tour | ATP World Tour Masters 1000 | 1996 ATP Tour | 2002 ATP Tour | 2006 ATP Tour | 2004 ATP Tour | 1990 ATP Tour | 2000 ATP Tour | 1998 ATP Tour | 1997 ATP Tour | 2007 ATP Tour | ATP World Tour Finals | 1999 ATP Tour | 1995 ATP Tour | 2005 ATP Tour | 1994 ATP Tour |