Year	mmol per litre
1980	4.543
1981	4.531
1982	4.515
1983	4.5
1984	4.477
1985	4.454
1986	4.431
1987	4.405
1988	4.38
1989	4.354
1990	4.33
1991	4.308
1992	4.284
1993	4.263
1994	4.242
1995	4.22
1996	4.2
1997	4.183
1998	4.164
1999	4.143
2000	4.123
2001	4.107
2002	4.089
2003	4.073
2004	4.058
2005	4.039
2006	4.019
2007	3.995
2008	3.974