Year	mmol per litre
1980	4.685
1981	4.681
1982	4.676
1983	4.67
1984	4.666
1985	4.663
1986	4.662
1987	4.659
1988	4.658
1989	4.652
1990	4.645
1991	4.641
1992	4.635
1993	4.627
1994	4.618
1995	4.608
1996	4.598
1997	4.587
1998	4.574
1999	4.562
2000	4.548
2001	4.535
2002	4.522
2003	4.509
2004	4.498
2005	4.487
2006	4.478
2007	4.467
2008	4.456