Year	mmol per litre
1980	5.18
1981	5.161
1982	5.138
1983	5.116
1984	5.092
1985	5.071
1986	5.048
1987	5.023
1988	4.997
1989	4.966
1990	4.931
1991	4.892
1992	4.844
1993	4.801
1994	4.76
1995	4.718
1996	4.674
1997	4.64
1998	4.61
1999	4.582
2000	4.556
2001	4.532
2002	4.51
2003	4.489
2004	4.471
2005	4.456
2006	4.441
2007	4.427
2008	4.414