Year	mmol per litre
1980	4.599
1981	4.595
1982	4.589
1983	4.582
1984	4.576
1985	4.573
1986	4.569
1987	4.566
1988	4.563
1989	4.562
1990	4.561
1991	4.561
1992	4.562
1993	4.566
1994	4.57
1995	4.575
1996	4.581
1997	4.588
1998	4.595
1999	4.601
2000	4.611
2001	4.618
2002	4.628
2003	4.637
2004	4.646
2005	4.653
2006	4.664
2007	4.674
2008	4.686