Year	mmol per litre
1980	4.926
1981	4.899
1982	4.871
1983	4.842
1984	4.814
1985	4.784
1986	4.752
1987	4.721
1988	4.692
1989	4.663
1990	4.635
1991	4.605
1992	4.575
1993	4.544
1994	4.519
1995	4.496
1996	4.477
1997	4.463
1998	4.45
1999	4.439
2000	4.434
2001	4.43
2002	4.43
2003	4.432
2004	4.437
2005	4.445
2006	4.455
2007	4.466
2008	4.477