Year	mmol per litre
1980	4.548
1981	4.545
1982	4.54
1983	4.535
1984	4.529
1985	4.525
1986	4.524
1987	4.526
1988	4.53
1989	4.537
1990	4.541
1991	4.549
1992	4.56
1993	4.578
1994	4.598
1995	4.615
1996	4.631
1997	4.645
1998	4.658
1999	4.672
2000	4.684
2001	4.695
2002	4.705
2003	4.715
2004	4.725
2005	4.733
2006	4.741
2007	4.751
2008	4.762