| Year | Value | | 2021 | 56.373072890625 | | 2020 | 56.5081015625 | | 2019 | 56.643125 | | 2018 | 56.77815625 | | 2017 | 56.902171875 | | 2016 | 57.03928125 | | 2015 | 57.1832265625 | | 2014 | 57.3168625 | | 2013 | 57.4504984375 | | 2012 | 57.584134375 | | 2011 | 57.7177703125 | | 2010 | 57.85140625 | | 2009 | 57.94890859375 | | 2008 | 58.0464109375 | | 2007 | 58.14391328125 | | 2006 | 58.241415625 | | 2005 | 58.33891796875 | | 2004 | 58.4364203125 | | 2003 | 58.53392265625 | | 2002 | 58.631425 | | 2001 | 58.72892734375 | | 2000 | 58.8264296875 | | 1999 | 58.91632890625 | | 1998 | 59.006228125 | | 1997 | 59.09612734375 | | 1996 | 59.1860265625 | | 1995 | 59.27592578125 | | 1994 | 59.365825 | | 1993 | 59.45572421875 | | 1992 | 59.5456234375 | | 1991 | 59.63552265625 | | 1990 | 59.725421875 |
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