Year	mmol per litre
1980	4.559
1981	4.562
1982	4.562
1983	4.567
1984	4.579
1985	4.593
1986	4.606
1987	4.618
1988	4.631
1989	4.638
1990	4.646
1991	4.654
1992	4.666
1993	4.678
1994	4.691
1995	4.701
1996	4.71
1997	4.722
1998	4.736
1999	4.751
2000	4.768
2001	4.787
2002	4.806
2003	4.826
2004	4.845
2005	4.862
2006	4.877
2007	4.894
2008	4.91