| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1901 | 62.8 | 58.1 | 70.4 | 74.1 | 82.5 | 91.6 | 92.6 | 94.5 | 85.3 | 79.0 | 68.0 | 57.6 | 76.5 |
| 1902 | 56.5 | 56.1 | 70.0 | 79.0 | 85.3 | 91.4 | 88.4 | 93.5 | 85.2 | 78.4 | 70.5 | 59.8 | 76.3 |
| 1903 | 57.2 | 56.7 | 67.0 | 75.9 | 78.3 | 82.6 | 88.9 | 90.2 | 86.6 | 75.6 | 67.4 | 61.3 | 74.1 |
| 1904 | 56.8 | 65.8 | 74.0 | 73.4 | 82.6 | 89.2 | 89.7 | 90.2 | 88.6 | 82.4 | 70.7 | 60.4 | 77.0 |
| 1905 | 52.5 | 50.3 | 73.3 | 74.6 | 84.1 | 89.1 | 87.6 | 91.0 | 88.2 | 76.4 | 70.4 | 51.7 | 74.2 |
| 1906 | 60.4 | 59.6 | 64.6 | 77.2 | 82.7 | 89.3 | 89.1 | 89.3 | 87.3 | 72.1 | 69.8 | 63.5 | 75.5 |
| 1907 | 66.9 | 78.3 | 70.7 | 78.5 | 88.7 | 92.4 | 95.1 | 91.1 | 76.8 | 63.8 | 61.1 | 78.6 | |
| 1908 | 59.6 | 60.7 | 75.1 | 77.1 | 81.8 | 88.8 | 90.2 | 89.3 | 85.5 | 76.3 | 71.0 | 63.3 | 76.6 |
| 1909 | 61.7 | 66.0 | 71.3 | 75.6 | 80.9 | 88.6 | 93.7 | 95.7 | 92.0 | 82.9 | 76.0 | 53.8 | 78.2 |
| 1910 | 61.7 | 58.4 | 77.5 | 75.8 | 80.5 | 86.8 | 90.4 | 93.0 | 92.9 | 81.7 | 69.9 | 79.1 | |
| 1911 | 65.5 | 68.0 | 73.9 | 73.3 | 83.0 | 93.9 | 87.7 | 90. | 93.8 | 77.9 | 63.4 | 56.5 | 77.3 |
| 1912 | 54.7 | 56.7 | 62.3 | 74.8 | 81.2 | 83.6 | 92.5 | 90.4 | 89.0 | 80.3 | 66.9 | 53.5 | 73.9 |
| 1913 | 58.1 | 59.5 | 65.4 | 75.7 | 81.3 | 86.9 | 93.3 | 94.4 | 81.4 | 73.4 | 74.0 | 55.7 | 75.0 |
| 1914 | 64.3 | 57.4 | 65.8 | 75.7 | 81.0 | 92.6 | 96.8 | 88.5 | 87.4 | 76.0 | 65.8 | 48.0 | 75.0 |
| 1915 | 53.0 | 60.8 | 55.6 | 75.5 | 82.9 | 91.5 | 90.9 | 87.2 | 86.7 | 79.6 | 71.1 | 61.6 | 74.7 |
| 1916 | 61.8 | 62.0 | 73.1 | 73.2 | 81.1 | 89.7 | 92.7 | 93.0 | 89.7 | 81.5 | 68.7 | 61.8 | 77.4 |
| 1917 | 60.1 | 64.4 | 68.9 | 73.7 | 76.9 | 91.1 | 94.4 | 96.9 | 88.7 | 78.4 | 70.2 | 54.6 | 76.6 |
| 1918 | 52.2 | 66.6 | 76.3 | 74.4 | 84.6 | 94.6 | 98.0 | 94.1 | 86.1 | 78.6 | 64.3 | 63.5 | 77.8 |
| 1919 | 58.9 | 63.2 | 73.6 | 80.9 | 82.1 | 87.8 | 93.6 | 94.7 | 90.1 | 82.9 | 73.2 | 66.0 | 79.0 |
| 1920 | 59.2 | 65.5 | 70.8 | 79.9 | 87.9 | 91.8 | 95.1 | 91.0 | 93.2 | 79.5 | 64.1 | 56.6 | 77.9 |
| 1921 | 62.4 | 63.5 | 72.0 | 70.1 | 82.7 | 90.4 | 93.1 | 97.0 | 93.7 | 84.0 | 78.3 | 69.0 | 79.8 |
| 1922 | 55.6 | 66.9 | 70.8 | 80.3 | 86.0 | 92.0 | 94.7 | 95.7 | 95.4 | 85.5 | 71.4 | 67.8 | 80.3 |
| 1923 | 69.5 | 60.4 | 62.8 | 75.6 | 80.7 | 91.8 | 95.2 | 97.7 | 88.8 | 78.6 | 66.9 | 62.4 | 77.6 |
| 1924 | 56.5 | 58.4 | 65.1 | 77.0 | 80.8 | 92.3 | 98.6 | 103.4 | 88.0 | 81.0 | 68.6 | 53.2 | 77.0 |
| 1925 | 54.5 | 63.8 | 69.3 | 76.3 | 80.4 | 92.3 | 94.0 | 92.8 | 89.1 | 71.4 | 61.9 | 53.5 | 75.0 |
| 1926 | 53.2 | 65.4 | 61.8 | 68.3 | 78.6 | 86.0 | 87.8 | 91.3 | 90.2 | 81.4 | 63.4 | 59.3 | 73.9 |
| 1927 | 59.7 | 65.1 | 65.5 | 76.5 | 82.7 | 85.1 | 90.2 | 94.0 | 88.9 | 81.3 | 74.8 | 53.5 | 76.5 |
| 1928 | 57.8 | 58.1 | 68.2 | 68.3 | 82.5 | 85.2 | 90.4 | 93.0 | 85.5 | 81.1 | 64.1 | 57.6 | 74.4 |
| 1929 | 59.0 | 49.0 | 70.5 | 77.8 | 77.5 | 86.7 | 89.1 | 93.6 | 88.8 | 79.0 | 57.8 | 58.2 | 74.1 |
| 1930 | 49.4 | 64.5 | 63.3 | 80.8 | 79.1 | 87.9 | 94.6 | 93.8 | 86.7 | 73.5 | 64.7 | 54.4 | 74.4 |