Year	mmol per litre
1980	5.381
1981	5.39
1982	5.392
1983	5.384
1984	5.369
1985	5.346
1986	5.317
1987	5.293
1988	5.27
1989	5.249
1990	5.222
1991	5.199
1992	5.183
1993	5.171
1994	5.163
1995	5.161
1996	5.16
1997	5.16
1998	5.162
1999	5.163
2000	5.164
2001	5.159
2002	5.152
2003	5.14
2004	5.13
2005	5.128
2006	5.119
2007	5.11
2008	5.099