Year	mmol per litre
1980	4.767
1981	4.763
1982	4.759
1983	4.758
1984	4.753
1985	4.744
1986	4.737
1987	4.732
1988	4.731
1989	4.732
1990	4.736
1991	4.74
1992	4.744
1993	4.751
1994	4.758
1995	4.768
1996	4.777
1997	4.789
1998	4.8
1999	4.812
2000	4.828
2001	4.842
2002	4.858
2003	4.872
2004	4.885
2005	4.896
2006	4.907
2007	4.917
2008	4.927