Year	mmol per litre
1980	5.175
1981	5.193
1982	5.205
1983	5.218
1984	5.231
1985	5.246
1986	5.257
1987	5.268
1988	5.278
1989	5.289
1990	5.3
1991	5.307
1992	5.32
1993	5.329
1994	5.334
1995	5.336
1996	5.337
1997	5.336
1998	5.334
1999	5.33
2000	5.322
2001	5.316
2002	5.306
2003	5.293
2004	5.267
2005	5.244
2006	5.221
2007	5.201
2008	5.18