Year	Kg per Square Metre
1980	26.77
1981	26.88
1982	26.97
1983	27.05
1984	27.11
1985	27.17
1986	27.22
1987	27.28
1988	27.35
1989	27.42
1990	27.48
1991	27.56
1992	27.63
1993	27.7
1994	27.78
1995	27.85
1996	27.93
1997	28.02
1998	28.11
1999	28.2
2000	28.3
2001	28.4
2002	28.51
2003	28.63
2004	28.74
2005	28.85
2006	28.96
2007	29.08
2008	29.2