Year	mmol per litre
1980	4.902
1981	4.914
1982	4.924
1983	4.932
1984	4.94
1985	4.949
1986	4.958
1987	4.967
1988	4.977
1989	4.989
1990	5.001
1991	5.013
1992	5.022
1993	5.032
1994	5.043
1995	5.055
1996	5.062
1997	5.066
1998	5.066
1999	5.06
2000	5.05
2001	5.036
2002	5.016
2003	4.994
2004	4.969
2005	4.945
2006	4.92
2007	4.895
2008	4.87