Year	mmol per litre
1980	5.554
1981	5.537
1982	5.519
1983	5.503
1984	5.486
1985	5.469
1986	5.452
1987	5.439
1988	5.43
1989	5.425
1990	5.418
1991	5.41
1992	5.39
1993	5.36
1994	5.327
1995	5.299
1996	5.262
1997	5.225
1998	5.196
1999	5.17
2000	5.151
2001	5.136
2002	5.128
2003	5.122
2004	5.121
2005	5.124
2006	5.133
2007	5.142
2008	5.145