| Period
| 2008 | 2009 | 2010 | 2011 | 2012 | | January | 10 | 13.55 | 13.5 | 10.5 | 45 | | February | 10 | 14 | 13.29 | 10.5 | 43.97 | | March | 10 | 14 | 13 | 11.27 | 38 | | January-March | 10 | 13.84 | 13.26 | 10.77 | 42.29 | | April | 10 | 14 | 12.8 | 12.37 | 36.07 | | May | 10 | 14 | 12.18 | 13.45 | | | June | 10 | 14 | 12 | 16.6 | | | April-June | 10 | 14 | 12.32 | 14.13 | | | January-June | 10 | 13.92 | 12.8 | 12.46 | | | July | 10.25 | 14 | 11.71 | 19.23 | | | August | 10.4 | 14 | 11.27 | 20.97 | | | September | 10.5 | 14 | 10.73 | 28.7 | | | July-September | 10.4 | 14 | 11.24 | 22.9 | | | January-September | 10.1 | 13.95 | 12.27 | 15.98 | | | October | 10.64 | 14 | 10.5 | 32.9 | | | November | 10.91 | 14 | 10.5 | 38.33 | | | December | 11.48 | 13.5 | 10.5 | 43.23 | | | October-December | 11.01 | 13.83 | 10.5 | 38.15 | | | January-December | 10.35 | 13.92 | 11.82 | 21.57 |
| Notes: * – calculated based on the calendar number of days.
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