start,end
1979-07-01,1979-08-01
1980-07-01,1980-08-01
1981-07-01,1981-08-01
1982-06-01,1982-07-01
1983-06-01,1983-07-01
1984-06-01,1984-06-01
1985-05-01,1985-06-01
1986-05-01,1986-06-01
1987-04-01,1987-05-01
1988-04-01,1988-05-01
1989-04-01,1989-05-01
1990-03-01,1990-04-01
1991-03-01,1991-04-01
1992-03-01,1992-04-01
1993-02-01,1993-03-01
1994-02-01,1994-03-01
1995-02-01,1995-02-01
1996-01-01,1996-02-01
1997-01-01,1997-02-01
1997-12-01,1998-01-01
1998-12-01,1999-01-01
1999-12-01,2000-01-01
2000-11-01,2000-12-01
2001-11-01,2001-12-01
2002-11-01,2002-12-01
2003-10-01,2003-11-01
2004-10-01,2004-11-01
2005-10-01,2005-11-01
2006-09-01,2006-10-01
2007-09-01,2007-10-01
2008-09-01,2008-09-01
2009-08-01,2009-09-01
2010-08-01,2010-09-01
2011-08-01,2011-08-01
2012-07-01,2012-08-01