Year	mmol per litre
1980	4.591
1981	4.579
1982	4.566
1983	4.552
1984	4.54
1985	4.527
1986	4.515
1987	4.505
1988	4.494
1989	4.486
1990	4.485
1991	4.485
1992	4.486
1993	4.489
1994	4.492
1995	4.493
1996	4.498
1997	4.505
1998	4.503
1999	4.5
2000	4.499
2001	4.498
2002	4.5
2003	4.502
2004	4.503
2005	4.505
2006	4.508
2007	4.512
2008	4.517