Year	mmol per litre
1980	5.067
1981	5.041
1982	5.016
1983	4.984
1984	4.951
1985	4.919
1986	4.891
1987	4.862
1988	4.837
1989	4.809
1990	4.781
1991	4.757
1992	4.737
1993	4.72
1994	4.699
1995	4.678
1996	4.66
1997	4.645
1998	4.631
1999	4.614
2000	4.599
2001	4.587
2002	4.575
2003	4.557
2004	4.546
2005	4.539
2006	4.539
2007	4.539
2008	4.539