Year	mmol per litre
1980	4.711
1981	4.693
1982	4.677
1983	4.658
1984	4.639
1985	4.632
1986	4.622
1987	4.617
1988	4.605
1989	4.602
1990	4.598
1991	4.593
1992	4.596
1993	4.597
1994	4.591
1995	4.579
1996	4.568
1997	4.55
1998	4.533
1999	4.516
2000	4.506
2001	4.502
2002	4.497
2003	4.493
2004	4.49
2005	4.489
2006	4.486
2007	4.482
2008	4.477