Year	mmol per litre
1980	5.426
1981	5.419
1982	5.414
1983	5.41
1984	5.406
1985	5.402
1986	5.396
1987	5.391
1988	5.382
1989	5.372
1990	5.359
1991	5.346
1992	5.326
1993	5.307
1994	5.291
1995	5.271
1996	5.255
1997	5.243
1998	5.232
1999	5.226
2000	5.221
2001	5.217
2002	5.216
2003	5.215
2004	5.212
2005	5.202
2006	5.193
2007	5.184
2008	5.175