Year	mmol per litre
1980	5.379
1981	5.364
1982	5.347
1983	5.333
1984	5.318
1985	5.302
1986	5.284
1987	5.264
1988	5.243
1989	5.218
1990	5.19
1991	5.149
1992	5.092
1993	5.029
1994	4.967
1995	4.911
1996	4.861
1997	4.822
1998	4.788
1999	4.762
2000	4.741
2001	4.725
2002	4.715
2003	4.711
2004	4.711
2005	4.713
2006	4.711
2007	4.709
2008	4.707