Year	mmol per litre
1980	4.68
1981	4.659
1982	4.636
1983	4.615
1984	4.593
1985	4.572
1986	4.551
1987	4.529
1988	4.507
1989	4.477
1990	4.446
1991	4.415
1992	4.382
1993	4.349
1994	4.319
1995	4.291
1996	4.266
1997	4.246
1998	4.227
1999	4.212
2000	4.198
2001	4.187
2002	4.176
2003	4.153
2004	4.13
2005	4.109
2006	4.089
2007	4.07
2008	4.053