Year	years
1970	7
1971	7
1972	7
1973	7
1974	7
1975	7
1976	7
1977	7
1978	7
1979	7
1980	7
1981	7
1982	7
1983	7
1984	7
1985	7
1986	6.5
1987	6.5
1988	6.5
1989	6
1990	6
1991	6
1992	6
1993	6
1994	6
1995	6
1996	6
1997	6
1998	7
1999	7
2000	7
2001	6.5
2002	6.5
2003	6.5
2004	6.5
2005	6.5
2006	6.5
2007	6
2008	6
2009	6
2010	6
2011	7
2012	7
2013	6
2014	6
2015	6.5
2016	6.5
2017	6.5
2018	6.5
2019	6.5
2020	6.5
2021	6.5
2022	6.5
2023	6.5