Year	mmol per litre
1980	4.83
1981	4.827
1982	4.827
1983	4.826
1984	4.825
1985	4.82
1986	4.81
1987	4.797
1988	4.783
1989	4.767
1990	4.75
1991	4.734
1992	4.718
1993	4.702
1994	4.682
1995	4.665
1996	4.65
1997	4.633
1998	4.619
1999	4.597
2000	4.579
2001	4.563
2002	4.549
2003	4.539
2004	4.531
2005	4.525
2006	4.521
2007	4.516
2008	4.512