Year	mmol per litre
1980	4.162
1981	4.142
1982	4.12
1983	4.099
1984	4.081
1985	4.065
1986	4.051
1987	4.037
1988	4.021
1989	4.005
1990	3.989
1991	3.97
1992	3.945
1993	3.917
1994	3.89
1995	3.873
1996	3.858
1997	3.846
1998	3.835
1999	3.823
2000	3.811
2001	3.8
2002	3.791
2003	3.787
2004	3.784
2005	3.781
2006	3.78
2007	3.779
2008	3.78