Year	Kg per Square Metre
1980	26.8
1981	26.8
1982	26.8
1983	26.8
1984	26.79
1985	26.77
1986	26.76
1987	26.74
1988	26.71
1989	26.69
1990	26.66
1991	26.61
1992	26.56
1993	26.5
1994	26.46
1995	26.45
1996	26.45
1997	26.46
1998	26.47
1999	26.46
2000	26.45
2001	26.46
2002	26.47
2003	26.47
2004	26.48
2005	26.48
2006	26.51
2007	26.51
2008	26.51