Year	mmol per litre
1980	5.022
1981	5.021
1982	5.013
1983	5.004
1984	4.996
1985	4.991
1986	4.988
1987	4.987
1988	4.989
1989	4.995
1990	5
1991	5.004
1992	5.011
1993	5.018
1994	5.024
1995	5.031
1996	5.035
1997	5.04
1998	5.043
1999	5.041
2000	5.037
2001	5.03
2002	5.019
2003	5.009
2004	4.998
2005	4.989
2006	4.98
2007	4.975
2008	4.969