Year	mmol per litre
1980	4.77
1981	4.75
1982	4.729
1983	4.71
1984	4.685
1985	4.662
1986	4.639
1987	4.614
1988	4.592
1989	4.573
1990	4.554
1991	4.537
1992	4.516
1993	4.495
1994	4.478
1995	4.461
1996	4.448
1997	4.439
1998	4.432
1999	4.426
2000	4.421
2001	4.416
2002	4.407
2003	4.395
2004	4.382
2005	4.369
2006	4.356
2007	4.342
2008	4.33