Year	mmol per litre
1980	4.186
1981	4.16
1982	4.132
1983	4.103
1984	4.07
1985	4.039
1986	4.006
1987	3.974
1988	3.945
1989	3.916
1990	3.889
1991	3.862
1992	3.836
1993	3.81
1994	3.789
1995	3.769
1996	3.755
1997	3.745
1998	3.737
1999	3.731
2000	3.728
2001	3.729
2002	3.734
2003	3.742
2004	3.752
2005	3.762
2006	3.772
2007	3.782
2008	3.794