Year	mmol per litre
1980	4.74
1981	4.721
1982	4.699
1983	4.676
1984	4.656
1985	4.638
1986	4.62
1987	4.606
1988	4.591
1989	4.575
1990	4.561
1991	4.548
1992	4.539
1993	4.533
1994	4.529
1995	4.527
1996	4.527
1997	4.528
1998	4.528
1999	4.528
2000	4.525
2001	4.519
2002	4.511
2003	4.504
2004	4.497
2005	4.491
2006	4.485
2007	4.479
2008	4.474