Year	Kg per Square Metre
1980	25.17
1981	25.17
1982	25.17
1983	25.16
1984	25.15
1985	25.14
1986	25.13
1987	25.11
1988	25.08
1989	25.04
1990	24.99
1991	24.9
1992	24.8
1993	24.68
1994	24.61
1995	24.57
1996	24.55
1997	24.55
1998	24.56
1999	24.59
2000	24.63
2001	24.69
2002	24.78
2003	24.87
2004	24.94
2005	25.01
2006	25.07
2007	25.13
2008	25.18