Year	mmol per litre
1980	5.024
1981	5.01
1982	4.994
1983	4.975
1984	4.959
1985	4.941
1986	4.921
1987	4.903
1988	4.887
1989	4.874
1990	4.865
1991	4.858
1992	4.857
1993	4.86
1994	4.867
1995	4.872
1996	4.881
1997	4.893
1998	4.91
1999	4.931
2000	4.955
2001	4.979
2002	5.004
2003	5.027
2004	5.052
2005	5.078
2006	5.103
2007	5.127
2008	5.15