Year	mmol per litre
1980	4.452
1981	4.453
1982	4.45
1983	4.45
1984	4.456
1985	4.464
1986	4.473
1987	4.482
1988	4.49
1989	4.493
1990	4.503
1991	4.512
1992	4.52
1993	4.525
1994	4.528
1995	4.531
1996	4.535
1997	4.54
1998	4.546
1999	4.55
2000	4.557
2001	4.567
2002	4.578
2003	4.591
2004	4.603
2005	4.612
2006	4.617
2007	4.624
2008	4.631