Year	mmol per litre
1980	4.473
1981	4.457
1982	4.44
1983	4.422
1984	4.408
1985	4.394
1986	4.379
1987	4.36
1988	4.342
1989	4.325
1990	4.307
1991	4.29
1992	4.27
1993	4.249
1994	4.228
1995	4.21
1996	4.194
1997	4.18
1998	4.169
1999	4.162
2000	4.16
2001	4.159
2002	4.159
2003	4.16
2004	4.158
2005	4.155
2006	4.156
2007	4.154
2008	4.151