Year	mmol per litre
1980	4.883
1981	4.87
1982	4.856
1983	4.844
1984	4.839
1985	4.832
1986	4.831
1987	4.828
1988	4.827
1989	4.829
1990	4.834
1991	4.842
1992	4.848
1993	4.856
1994	4.858
1995	4.863
1996	4.859
1997	4.852
1998	4.85
1999	4.848
2000	4.842
2001	4.837
2002	4.827
2003	4.827
2004	4.821
2005	4.817
2006	4.811
2007	4.806
2008	4.8