Year	mmol per litre
1980	5.163
1981	5.147
1982	5.132
1983	5.117
1984	5.102
1985	5.085
1986	5.071
1987	5.054
1988	5.036
1989	5.016
1990	4.992
1991	4.961
1992	4.909
1993	4.858
1994	4.812
1995	4.774
1996	4.738
1997	4.709
1998	4.687
1999	4.671
2000	4.661
2001	4.655
2002	4.66
2003	4.664
2004	4.675
2005	4.682
2006	4.69
2007	4.7
2008	4.707