Year	mmol per litre
1980	4.832
1981	4.823
1982	4.816
1983	4.814
1984	4.812
1985	4.811
1986	4.809
1987	4.811
1988	4.814
1989	4.817
1990	4.823
1991	4.829
1992	4.832
1993	4.833
1994	4.832
1995	4.83
1996	4.832
1997	4.83
1998	4.825
1999	4.823
2000	4.822
2001	4.82
2002	4.82
2003	4.821
2004	4.815
2005	4.807
2006	4.801
2007	4.794
2008	4.789