Year	mmol per litre
1980	5.438
1981	5.421
1982	5.404
1983	5.389
1984	5.372
1985	5.353
1986	5.336
1987	5.318
1988	5.299
1989	5.28
1990	5.257
1991	5.229
1992	5.196
1993	5.154
1994	5.109
1995	5.066
1996	5.019
1997	4.977
1998	4.937
1999	4.903
2000	4.871
2001	4.844
2002	4.825
2003	4.811
2004	4.804
2005	4.799
2006	4.798
2007	4.8
2008	4.802