Year	mmol per litre
1980	4.648
1981	4.652
1982	4.658
1983	4.662
1984	4.667
1985	4.675
1986	4.685
1987	4.694
1988	4.702
1989	4.709
1990	4.715
1991	4.723
1992	4.731
1993	4.74
1994	4.751
1995	4.763
1996	4.774
1997	4.786
1998	4.8
1999	4.815
2000	4.83
2001	4.846
2002	4.861
2003	4.873
2004	4.882
2005	4.89
2006	4.898
2007	4.905
2008	4.911