Year	mmol per litre
1980	4.688
1981	4.694
1982	4.698
1983	4.701
1984	4.703
1985	4.703
1986	4.699
1987	4.695
1988	4.689
1989	4.682
1990	4.677
1991	4.672
1992	4.666
1993	4.66
1994	4.656
1995	4.653
1996	4.651
1997	4.65
1998	4.647
1999	4.644
2000	4.641
2001	4.636
2002	4.63
2003	4.625
2004	4.618
2005	4.611
2006	4.603
2007	4.592
2008	4.581