Year	mmol per litre
1980	5.353
1981	5.351
1982	5.342
1983	5.338
1984	5.334
1985	5.333
1986	5.334
1987	5.336
1988	5.338
1989	5.338
1990	5.331
1991	5.32
1992	5.307
1993	5.291
1994	5.274
1995	5.259
1996	5.246
1997	5.235
1998	5.228
1999	5.223
2000	5.218
2001	5.212
2002	5.206
2003	5.199
2004	5.191
2005	5.181
2006	5.172
2007	5.163
2008	5.154