Year	mmol per litre
1980	4.551
1981	4.543
1982	4.534
1983	4.526
1984	4.518
1985	4.51
1986	4.502
1987	4.495
1988	4.487
1989	4.481
1990	4.474
1991	4.466
1992	4.46
1993	4.455
1994	4.449
1995	4.443
1996	4.437
1997	4.433
1998	4.428
1999	4.421
2000	4.415
2001	4.408
2002	4.401
2003	4.394
2004	4.386
2005	4.38
2006	4.374
2007	4.368
2008	4.363