Year	mmol per litre
1980	4.789
1981	4.77
1982	4.751
1983	4.734
1984	4.719
1985	4.707
1986	4.694
1987	4.684
1988	4.674
1989	4.666
1990	4.655
1991	4.641
1992	4.626
1993	4.601
1994	4.576
1995	4.556
1996	4.54
1997	4.528
1998	4.519
1999	4.512
2000	4.505
2001	4.5
2002	4.499
2003	4.498
2004	4.498
2005	4.502
2006	4.508
2007	4.518
2008	4.528