| Year | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual |
| 1931 | 71.0 | 71.0 | 79.0 | 83.0 | 85.0 | 95.0 | 99.0 | 94.0 | 97.0 | 92.0 | 81.0 | 79.0 | 99.0 |
| 1932 | 78.0 | 83.0 | 84.0 | 85.0 | 89.0 | 96.0 | 102.0 | 101.0 | 98.0 | 87.0 | 74.0 | 69.0 | 102.0 |
| 1933 | 74.0 | 77.0 | 79.0 | 87.0 | 90.0 | 97.0 | 99.0 | 94.0 | 95.0 | 87.0 | 80.0 | 79.0 | 99.0 |
| 1934 | 71.0 | 71.0 | 81.0 | 85.0 | 90.0 | 98.0 | 102.0 | 100.0 | 95.0 | 89.0 | 84.0 | 69.0 | 102.0 |
| 1935 | 78.0 | 75.0 | 88.0 | 84.0 | 86.0 | 90.0 | 98.0 | 104.0 | 95.0 | 89.0 | 85.0 | 68.0 | 104.0 |
| 1936 | 78.0 | 78.0 | 84.0 | 88.0 | 85.0 | 103.0 | 96.0 | 104.0 | 94.0 | 88.0 | 84.0 | 73.0 | 104.0 |
| 1937 | 75.0 | 80.0 | 78.0 | 83.0 | 89.0 | 99.0 | 98.0 | 100.0 | 95.0 | 89.0 | 78.0 | 71.0 | 100.0 |
| 1938 | 74.0 | 77.0 | 83.0 | 84.0 | 88.0 | 94.0 | 95.0 | 98.0 | 96.0 | 99.0 | 84.0 | 77.0 | 99.0 |
| 1939 | 75.0 | 75.0 | 83.0 | 88.0 | 89.0 | 95.0 | 104.0 | 103.0 | 100.0 | 92.0 | 77.0 | 79.0 | 104.0 |
| 1940 | 71.0 | 85.0 | 83.0 | 85.0 | 87.0 | 90.0 | 95.0 | 94.0 | 92.0 | 88.0 | 78.0 | 72.0 | 95.0 |
| 1941 | 71.0 | 70.0 | 80.0 | 85.0 | 88.0 | 91.0 | 93.0 | 95.0 | 93.0 | 88.0 | 77.0 | 74.0 | 95.0 |
| 1942 | 75.0 | 74.0 | 85.0 | 84.0 | 88.0 | 93.0 | 96.0 | 97.0 | 91.0 | 88.0 | 83.0 | 79.0 | 97.0 |
| 1943 | 83.0 | 77.0 | 81.0 | 88.0 | 91.0 | 97.0 | 102.0 | 103.0 | 95.0 | 85.0 | 83.0 | 77.0 | 103.0 |
| 1944 | 72.0 | 77.0 | 80.0 | 86.0 | 88.0 | 95.0 | 103.0 | 100.0 | 94.0 | 90.0 | 82.0 | 72.0 | 103.0 |
| 1945 | 71.0 | 83.0 | 85.0 | 86.0 | 90.0 | 97.0 | 95.0 | 99.0 | 97.0 | 85.0 | 86.0 | 74.0 | 99.0 |
| 1946 | 75.0 | 76.0 | 93.0 | 86.0 | 88.0 | 95.0 | 99.0 | 99.0 | 94.0 | 86.0 | 82.0 | 77.0 | 99.0 |
| 1947 | 80.0 | 80.0 | 79.0 | 87.0 | 92.0 | 94.0 | 99.0 | 108.0 | 105.0 | 95.0 | 83.0 | 75.0 | 108.0 |
| 1948 | 76.0 | 84.0 | 83.0 | 90.0 | 90.0 | 97.0 | 99.0 | 104.0 | 100.0 | 92.0 | 87.0 | 80.0 | 104.0 |
| 1949 | 80.0 | 81.0 | 83.0 | 88.0 | 93.0 | 96.0 | 99.0 | 97.0 | 96.0 | 89.0 | 85.0 | 78.0 | 99.0 |
| 1950 | 84.0 | 83.0 | 87.0 | 84.0 | 90.0 | 94.0 | 93.0 | 97.0 | 94.0 | 88.0 | 86.0 | 81.0 | 97.0 |
| 1951 | 78.0 | 82.0 | 84.0 | 89.0 | 95.0 | 95.0 | 102.0 | 106.0 | 104.0 | 91.0 | 87.0 | 82.0 | 106.0 |
| 1952 | 82.0 | 80.0 | 84.0 | 83.0 | 91.0 | 97.0 | 97.0 | 100.0 | 98.0 | 93.0 | 84.0 | 78.0 | 100.0 |
| 1953 | 76.0 | 78.0 | 88.0 | 85.0 | 93.0 | 101.0 | 96.0 | 98.0 | 100.0 | 98.0 | 80.0 | 82.0 | 101.0 |
| 1954 | 80.0 | 83.0 | 87.0 | 87.0 | 90.0 | 97.0 | 107.0 | 110.0 | 103.0 | 98.0 | 80.0 | 80.0 | 110.0 |
| 1955 | 73.0 | 78.0 | 91.0 | 91.0 | 95.0 | 98.0 | 102.0 | 101.0 | 98.0 | 95.0 | 88.0 | 84.0 | 102.0 |
| 1956 | 83.0 | 84.0 | 86.0 | 87.0 | 94.0 | 99.0 | 103.0 | 108.0 | 103.0 | 97.0 | 84.0 | 85.0 | 108.0 |
| 1957 | 82.0 | 87.0 | 81.0 | 86.0 | 91.0 | 95.0 | 104.0 | 101.0 | 98.0 | 90.0 | 85.0 | 77.0 | 104.0 |
| 1958 | 72.0 | 75.0 | 81.0 | 88.0 | 100.0 | 98.0 | 99.0 | 106.0 | 97.0 | 90.0 | 85.0 | 74.0 | 106.0 |
| 1959 | 75.0 | 82.0 | 82.0 | 90.0 | 94.0 | 98.0 | 99.0 | 99.0 | 96.0 | 92.0 | 80.0 | 73.0 | 99.0 |
| 1960 | 78.0 | 82.0 | 87.0 | 90.0 | 95.0 | 103.0 | 102.0 | 100.0 | 99.0 | 91.0 | 84.0 | 76.0 | 103.0 |