Year	mmol per litre
1980	4.858
1981	4.861
1982	4.859
1983	4.855
1984	4.851
1985	4.848
1986	4.851
1987	4.853
1988	4.852
1989	4.853
1990	4.853
1991	4.853
1992	4.856
1993	4.859
1994	4.863
1995	4.871
1996	4.875
1997	4.88
1998	4.883
1999	4.883
2000	4.883
2001	4.881
2002	4.876
2003	4.868
2004	4.862
2005	4.854
2006	4.847
2007	4.84
2008	4.835