Year	mmol per litre
1980	5.525
1981	5.498
1982	5.475
1983	5.453
1984	5.431
1985	5.413
1986	5.395
1987	5.375
1988	5.349
1989	5.327
1990	5.304
1991	5.279
1992	5.255
1993	5.23
1994	5.205
1995	5.183
1996	5.159
1997	5.139
1998	5.123
1999	5.103
2000	5.087
2001	5.067
2002	5.048
2003	5.035
2004	5.019
2005	5.008
2006	5.002
2007	4.995
2008	4.988