Year	mmol per litre
1980	4.575
1981	4.577
1982	4.58
1983	4.581
1984	4.582
1985	4.585
1986	4.586
1987	4.588
1988	4.589
1989	4.588
1990	4.589
1991	4.586
1992	4.582
1993	4.579
1994	4.573
1995	4.567
1996	4.559
1997	4.55
1998	4.541
1999	4.531
2000	4.519
2001	4.505
2002	4.487
2003	4.466
2004	4.443
2005	4.419
2006	4.393
2007	4.367
2008	4.34