Year	mmol per litre
1980	5.028
1981	5.012
1982	4.996
1983	4.984
1984	4.973
1985	4.959
1986	4.95
1987	4.947
1988	4.945
1989	4.941
1990	4.94
1991	4.936
1992	4.932
1993	4.927
1994	4.921
1995	4.916
1996	4.902
1997	4.886
1998	4.871
1999	4.857
2000	4.846
2001	4.838
2002	4.83
2003	4.825
2004	4.82
2005	4.817
2006	4.815
2007	4.812
2008	4.809