Year	Kg per Square Metre
1980	25
1981	25
1982	25
1983	24.99
1984	24.99
1985	24.98
1986	24.98
1987	24.97
1988	24.97
1989	24.98
1990	24.99
1991	24.99
1992	24.99
1993	24.99
1994	24.97
1995	24.97
1996	24.95
1997	24.95
1998	24.95
1999	24.97
2000	25.02
2001	25.09
2002	25.17
2003	25.28
2004	25.41
2005	25.55
2006	25.7
2007	25.85
2008	26.01