Year	mmol per litre
1980	4.856
1981	4.857
1982	4.855
1983	4.854
1984	4.852
1985	4.853
1986	4.855
1987	4.857
1988	4.859
1989	4.864
1990	4.868
1991	4.874
1992	4.881
1993	4.89
1994	4.901
1995	4.912
1996	4.92
1997	4.925
1998	4.928
1999	4.931
2000	4.935
2001	4.939
2002	4.943
2003	4.946
2004	4.949
2005	4.952
2006	4.952
2007	4.953
2008	4.953