Year	mmol per litre
1980	5.883
1981	5.862
1982	5.834
1983	5.804
1984	5.775
1985	5.745
1986	5.714
1987	5.686
1988	5.659
1989	5.628
1990	5.598
1991	5.577
1992	5.558
1993	5.536
1994	5.512
1995	5.495
1996	5.48
1997	5.472
1998	5.466
1999	5.459
2000	5.449
2001	5.441
2002	5.427
2003	5.41
2004	5.394
2005	5.377
2006	5.354
2007	5.337
2008	5.32