Year	mmol per litre
1980	4.879
1981	4.877
1982	4.874
1983	4.872
1984	4.871
1985	4.869
1986	4.869
1987	4.87
1988	4.871
1989	4.871
1990	4.871
1991	4.871
1992	4.873
1993	4.874
1994	4.877
1995	4.878
1996	4.88
1997	4.881
1998	4.881
1999	4.881
2000	4.881
2001	4.878
2002	4.874
2003	4.87
2004	4.865
2005	4.858
2006	4.851
2007	4.843
2008	4.835