Year	mmol per litre
1980	4.583
1981	4.576
1982	4.57
1983	4.566
1984	4.561
1985	4.555
1986	4.55
1987	4.541
1988	4.525
1989	4.507
1990	4.486
1991	4.467
1992	4.441
1993	4.407
1994	4.372
1995	4.341
1996	4.313
1997	4.291
1998	4.273
1999	4.252
2000	4.222
2001	4.191
2002	4.171
2003	4.156
2004	4.14
2005	4.128
2006	4.116
2007	4.106
2008	4.096