Year	mmol per litre
1980	4.894
1981	4.879
1982	4.862
1983	4.844
1984	4.822
1985	4.801
1986	4.778
1987	4.757
1988	4.735
1989	4.715
1990	4.694
1991	4.674
1992	4.656
1993	4.639
1994	4.623
1995	4.609
1996	4.594
1997	4.587
1998	4.58
1999	4.577
2000	4.578
2001	4.576
2002	4.571
2003	4.567
2004	4.566
2005	4.563
2006	4.557
2007	4.551
2008	4.546