Year	mmol per litre
1980	4.577
1981	4.568
1982	4.564
1983	4.561
1984	4.562
1985	4.563
1986	4.564
1987	4.567
1988	4.569
1989	4.574
1990	4.58
1991	4.583
1992	4.589
1993	4.591
1994	4.593
1995	4.593
1996	4.592
1997	4.591
1998	4.589
1999	4.585
2000	4.58
2001	4.572
2002	4.566
2003	4.556
2004	4.55
2005	4.541
2006	4.54
2007	4.533
2008	4.528