Year	mmol per litre
1980	5.281
1981	5.278
1982	5.272
1983	5.256
1984	5.24
1985	5.223
1986	5.207
1987	5.198
1988	5.188
1989	5.176
1990	5.161
1991	5.152
1992	5.145
1993	5.14
1994	5.138
1995	5.13
1996	5.124
1997	5.113
1998	5.103
1999	5.091
2000	5.07
2001	5.041
2002	5.002
2003	4.961
2004	4.923
2005	4.889
2006	4.855
2007	4.823
2008	4.795