Year	mmol per litre
1980	4.484
1981	4.476
1982	4.469
1983	4.465
1984	4.461
1985	4.458
1986	4.455
1987	4.453
1988	4.451
1989	4.451
1990	4.451
1991	4.451
1992	4.455
1993	4.458
1994	4.465
1995	4.473
1996	4.483
1997	4.494
1998	4.506
1999	4.518
2000	4.532
2001	4.548
2002	4.566
2003	4.583
2004	4.602
2005	4.62
2006	4.639
2007	4.658
2008	4.677