Year	Kg per Square Metre
1980	25.32
1981	25.33
1982	25.35
1983	25.37
1984	25.4
1985	25.42
1986	25.44
1987	25.44
1988	25.44
1989	25.42
1990	25.4
1991	25.35
1992	25.27
1993	25.17
1994	25.1
1995	25.07
1996	25.12
1997	25.22
1998	25.34
1999	25.45
2000	25.58
2001	25.71
2002	25.84
2003	25.97
2004	26.12
2005	26.25
2006	26.37
2007	26.49
2008	26.61