| July | August | September | October | November | December | |
| 1993 | 17.39 | 17.39 | 17.39 | 17.39 | 17.39 | 17.39 |
| 1994 | 32.44 | 32.44 | 32.44 | 32.44 | 32.44 | 32.44 |
| 1995 | 45.52 | 45.52 | 45.52 | 45.52 | 45.52 | 45.52 |
| 1996 | 56.97 | 56.97 | 56.97 | 56.97 | 56.97 | 56.97 |
| 1997 | 66.95 | 66.95 | 66.95 | 66.95 | 66.95 | 66.95 |
| 1998 | 68.32 | 68.18 | 68.04 | 67.90 | 67.77 | 67.63 |
| 1999 | 70.91 | 70.76 | 70.62 | 70.48 | 70.34 | 70.20 |
| 2000 | 73.74 | 75.58 | 73.43 | 73.28 | 73.14 | 73.00 |
| 2001 | 77.01 | 76.84 | 76.68 | 76.53 | 76.37 | 76.22 |
| 2002 | 80.63 | 80.45 | 80.27 | 80.11 | 79.94 | 79.78 |
| 2003 | 84.47 | 84.28 | 84.09 | 83.90 | 83.73 | 83.56 |
| 2004 | 88.25 | 88.04 | 87.83 | 89.79 | 89.50 | 89.22 |
| 2005 | 91.69 | 91.46 | 91.25 | 93.41 | 93.07 | 92.75 |
| 2006 | 94.79 | 94.58 | 94.39 | 96.70 | 96.27 | 95.89 |
| 2007 | 97.21 | 97.21 | 97.21 | 97.21 | 97.21 | 97.21 |
| January | February | March | April | May | June | |
| 1993 | 17.39 |
17.39 | 17.39 | 17.39 | 17.39 | 17.39 |
| 1994 | 32.44 | 32.44 | 32.44 | 32.44 | 32.44 | 32.44 |
| 1995 | 45.52 | 45.52 | 45.52 | 45.52 | 45.52 | 45.52 |
| 1996 | 56.97 | 56.97 | 56.97 | 56.97 | 56.97 | 56.97 |
| 1997 | 66.95 | 66.95 | 66.95 | 66.95 | 66.95 | 66.95 |
| 1998 | 69.23 | 69.08 | 68.92 | 68.77 | 68.62 | 68.47 |
| 1999 | 71.86 | 71.70 | 71.53 | 71.37 | 71.22 | 71.06 |
| 2000 | 74.74 | 74.56 | 74.39 | 74.22 | 74.05 | 73.89 |
| 2001 | 78.09 | 77.89 | 77.71 | 77.52 | 88.35 | 77.17 |
| 2002 | 81.82 | 81.60 | 81.40 | 81.19 | 81.00 | 80.81 |
| 2003 | 85.82 | 85.57 | 85.33 | 85.11 | 84.89 | 84.68 |
| 2004 | 89.79 | 89.50 | 89.22 | 88.96 | 88.72 | 88.48 |
| 2005 | 93.41 | 93.07 | 92.75 | 92.46 | 92.18 | 91.93 |
| 2006 | 96.70 | 96.27 | 95.89 | 95.57 | 95.28 | 95.02 |
| 2007 | 97.21 | 97.21 | 97.21 | 97.21 | 97.21 | 97.21 |