Year	mmol per litre
1980	4.265
1981	4.256
1982	4.249
1983	4.243
1984	4.241
1985	4.24
1986	4.238
1987	4.234
1988	4.23
1989	4.224
1990	4.218
1991	4.208
1992	4.193
1993	4.177
1994	4.163
1995	4.152
1996	4.14
1997	4.129
1998	4.119
1999	4.113
2000	4.109
2001	4.104
2002	4.099
2003	4.093
2004	4.085
2005	4.079
2006	4.072
2007	4.065
2008	4.059