Year	mmol per litre
1980	4.885
1981	4.887
1982	4.89
1983	4.89
1984	4.892
1985	4.894
1986	4.898
1987	4.899
1988	4.904
1989	4.909
1990	4.915
1991	4.922
1992	4.923
1993	4.924
1994	4.927
1995	4.928
1996	4.928
1997	4.924
1998	4.92
1999	4.91
2000	4.897
2001	4.883
2002	4.866
2003	4.848
2004	4.831
2005	4.815
2006	4.8
2007	4.785
2008	4.769