Year	mmol per litre
1980	4.999
1981	4.991
1982	4.982
1983	4.974
1984	4.966
1985	4.955
1986	4.942
1987	4.934
1988	4.928
1989	4.923
1990	4.925
1991	4.936
1992	4.955
1993	4.979
1994	5.009
1995	5.043
1996	5.072
1997	5.098
1998	5.119
1999	5.136
2000	5.153
2001	5.164
2002	5.169
2003	5.167
2004	5.165
2005	5.164
2006	5.162
2007	5.163
2008	5.166