Year	mmol per litre
1980	4.868
1981	4.872
1982	4.875
1983	4.876
1984	4.881
1985	4.884
1986	4.889
1987	4.895
1988	4.899
1989	4.903
1990	4.907
1991	4.909
1992	4.912
1993	4.917
1994	4.918
1995	4.918
1996	4.917
1997	4.917
1998	4.913
1999	4.905
2000	4.893
2001	4.874
2002	4.855
2003	4.842
2004	4.832
2005	4.822
2006	4.816
2007	4.809
2008	4.804