Year	mmol per litre
1980	4.734
1981	4.718
1982	4.694
1983	4.667
1984	4.638
1985	4.609
1986	4.582
1987	4.561
1988	4.541
1989	4.518
1990	4.497
1991	4.48
1992	4.47
1993	4.465
1994	4.463
1995	4.463
1996	4.465
1997	4.466
1998	4.465
1999	4.467
2000	4.461
2001	4.452
2002	4.443
2003	4.434
2004	4.429
2005	4.415
2006	4.403
2007	4.394
2008	4.386