Year	mmol per litre
1980	4.821
1981	4.821
1982	4.822
1983	4.821
1984	4.82
1985	4.819
1986	4.819
1987	4.818
1988	4.817
1989	4.815
1990	4.816
1991	4.816
1992	4.819
1993	4.824
1994	4.83
1995	4.835
1996	4.829
1997	4.826
1998	4.825
1999	4.825
2000	4.821
2001	4.808
2002	4.787
2003	4.764
2004	4.74
2005	4.717
2006	4.694
2007	4.673
2008	4.653