Year	mmol per litre
1980	4.857
1981	4.846
1982	4.833
1983	4.819
1984	4.798
1985	4.781
1986	4.762
1987	4.734
1988	4.712
1989	4.697
1990	4.682
1991	4.666
1992	4.649
1993	4.625
1994	4.601
1995	4.578
1996	4.563
1997	4.557
1998	4.55
1999	4.546
2000	4.537
2001	4.534
2002	4.531
2003	4.528
2004	4.525
2005	4.522
2006	4.519
2007	4.515
2008	4.513