Year	mmol per litre
1980	4.808
1981	4.804
1982	4.8
1983	4.795
1984	4.789
1985	4.781
1986	4.771
1987	4.765
1988	4.761
1989	4.758
1990	4.763
1991	4.777
1992	4.799
1993	4.829
1994	4.864
1995	4.903
1996	4.937
1997	4.966
1998	4.99
1999	5.009
2000	5.027
2001	5.038
2002	5.042
2003	5.038
2004	5.033
2005	5.029
2006	5.025
2007	5.024
2008	5.024