Year	mmol per litre
1980	5.398
1981	5.389
1982	5.38
1983	5.369
1984	5.36
1985	5.347
1986	5.338
1987	5.328
1988	5.317
1989	5.307
1990	5.296
1991	5.274
1992	5.248
1993	5.215
1994	5.183
1995	5.155
1996	5.127
1997	5.106
1998	5.084
1999	5.062
2000	5.048
2001	5.035
2002	5.024
2003	5.013
2004	5.005
2005	4.997
2006	4.986
2007	4.98
2008	4.972