Year	mmol per litre
1980	4.773
1981	4.772
1982	4.769
1983	4.767
1984	4.764
1985	4.766
1986	4.769
1987	4.773
1988	4.777
1989	4.783
1990	4.791
1991	4.8
1992	4.812
1993	4.825
1994	4.842
1995	4.859
1996	4.873
1997	4.884
1998	4.896
1999	4.906
2000	4.919
2001	4.931
2002	4.943
2003	4.952
2004	4.957
2005	4.961
2006	4.963
2007	4.963
2008	4.963