2008-06-12   6.250
2008-07-30   6.350
2009-05-06   6.550
2010-06-12   6.640
2011-03-27   6.630
2012-06-13   6.650
2013-07-19   6.500
2014-07-21   6.520
2014-09-23   6.410
2015-05-25   6.530