Year	mmol per litre
1980	4.723
1981	4.705
1982	4.685
1983	4.663
1984	4.642
1985	4.621
1986	4.602
1987	4.583
1988	4.563
1989	4.546
1990	4.528
1991	4.516
1992	4.504
1993	4.491
1994	4.479
1995	4.467
1996	4.455
1997	4.449
1998	4.445
1999	4.444
2000	4.45
2001	4.45
2002	4.448
2003	4.449
2004	4.449
2005	4.45
2006	4.452
2007	4.455
2008	4.456