Monthly Thousands Of Service Hours
1921-07-01 309538.
1921-08-01 335807.
1921-09-01 328288.
1921-10-01 350976.
1921-11-01 328012.
1921-12-01 310547.
1922-01-01 292919.
1922-02-01 272065.
1922-03-01 314461.
1922-04-01 294002.
1922-05-01 319069.
1922-06-01 328681.
1922-07-01 293729.
1922-08-01 348284.
1922-09-01 362922.
1922-10-01 391831.
1922-11-01 375429.
1922-12-01 368692.
1923-01-01 375162.
1923-02-01 336780.
1923-03-01 386624.
1923-04-01 370254.
1923-05-01 395264.
1923-06-01 393970.
1923-07-01 395042.
1923-08-01 411540.
1923-09-01 378665.
1923-10-01 409504.
1923-11-01 368713.
1923-12-01 341646.
1924-01-01 350245.
1924-02-01 330780.
1924-03-01 352571.
1924-04-01 348309.
1924-05-01 353867.
1924-06-01 334572.
1924-07-01 346254.
1924-08-01 350013.
1924-09-01 349224.
1924-10-01 376604.
1924-11-01 337567.
1924-12-01 343423.
1925-01-01 347615.
1925-02-01 311835.
1925-03-01 341865.
1925-04-01 339103.
1925-05-01 343365.
1925-06-01 349106.
1925-07-01 356997.
1925-08-01 356999.
1925-09-01 350232.
1925-10-01 373996.
1925-11-01 342086.
1925-12-01 346976.
1926-01-01 337030.
1926-02-01 315168.
1926-03-01 357259.
1926-04-01 349131.
1926-05-01 354561.
1926-06-01 361489.
1926-07-01 369022.
1926-08-01 371342.
1926-09-01 363104.
1926-10-01 377978.
1926-11-01 356760.
1926-12-01 353575.
1927-01-01 337980.
1927-02-01 308187.
1927-03-01 351255.
1927-04-01 343597.
1927-05-01 352007.
1927-06-01 358074.
1927-07-01 350777.
1927-08-01 363711.
1927-09-01 344736.
1927-10-01 356202.
1927-11-01 328921.
1927-12-01 319877.
1928-01-01 310953.
1928-02-01 294389.
1928-03-01 325181.
1928-04-01 313652.
1928-05-01 338264.
1928-06-01 335483.
1928-07-01 332585.
1928-08-01 349127.
1928-09-01 324244.
1928-10-01 354518.
1928-11-01 320800.
1928-12-01 305625.
1929-01-01 315240.
1929-02-01 287475.
1929-03-01 321954.
1929-04-01 326000.
1929-05-01 341684.
1929-06-01 332940.
1929-07-01 347473.
1929-08-01 355769.
1929-09-01 330463.
1929-10-01 358144.
1929-11-01 317266.
1929-12-01 303627.
1930-01-01 303491.
1930-02-01 269841.
1930-03-01 297064.
1930-04-01 298952.
1930-05-01 306026.
1930-06-01 286647.
1930-07-01 285928.
1930-08-01 281501.
1930-09-01 268621.
1930-10-01 278234.
1930-11-01 242074.
1930-12-01 243573.
1931-01-01 240460.
1931-02-01 214549.
1931-03-01 239619.
1931-04-01 238730.
1931-05-01 237741.
1931-06-01 234276.
1931-07-01 234281.
1931-08-01 225761.
1931-09-01 213979.
1931-10-01 217125.
1931-11-01 189475.
1931-12-01 189763.
1932-01-01 182497.
1932-02-01 175202.
1932-03-01 191796.
1932-04-01 180774.
1932-05-01 179096.
1932-06-01 172381.
1932-07-01 162711.
1932-08-01 165450.
1932-09-01 161131.
1932-10-01 171454.
1932-11-01 161670.
1932-12-01 160793.
1933-01-01 152231.
1933-02-01 139232.
1933-03-01 149980.
1933-04-01 144232.
1933-05-01 156219.
1933-06-01 159183.
1933-07-01 165937.
1933-08-01 178130.
1933-09-01 171519.
1933-10-01 177263.
1933-11-01 162642.
1933-12-01 158145.
1934-01-01 164431.
1934-02-01 153775.
1934-03-01 176916.
1934-04-01 169459.
1934-05-01 182530.
1934-06-01 181736.
1934-07-01 178597.
1934-08-01 182371.
1934-09-01 167890.
1934-10-01 180946.
1934-11-01 162376.
1934-12-01 160828.
1935-01-01 170962.
1935-02-01 154191.
1935-03-01 170086.
1935-04-01 167183.
1935-05-01 174472.
1935-06-01 171584.
1935-07-01 177531.
1935-08-01 179423.
1935-09-01 169398.
1935-10-01 186886.
1935-11-01 169486.
1935-12-01 170927.
1936-01-01 180861.
1936-02-01 183398.
1936-03-01 188481.
1936-04-01 188648.
1936-05-01 190070.
1936-06-01 193329.
1936-07-01 200052.
1936-08-01 198736.
1936-09-01 198372.
1936-10-01 211777.
1936-11-01 192158.
1936-12-01 201178.
1937-01-01 196164.
1937-02-01 186726.
1937-03-01 211948.
1937-04-01 208608.
1937-05-01 211726.
1937-06-01 216817.
1937-07-01 218606.
1937-08-01 214580.
1937-09-01 203682.
1937-10-01 205818.
1937-11-01 184853.
1937-12-01 179328.
1938-01-01 167502.
1938-02-01 150797.
1938-03-01 169830.
1938-04-01 158478.
1938-05-01 157443.
1938-06-01 161308.
1938-07-01 162578.
1938-08-01 173633.
1938-09-01 171288.
1938-10-01 180429.
1938-11-01 170024.
1938-12-01 170726.
1939-01-01 167647.
1939-02-01 155288.
1939-03-01 177901.
1939-04-01 165193.
1939-05-01 175803.
1939-06-01 180939.
1939-07-01 179094.
1939-08-01 189008.
1939-09-01 185208.
1939-10-01 201294.
1939-11-01 188135.
1939-12-01 180939.
1940-01-01 186767.
1940-02-01 171331.
1940-03-01 180381.
1940-04-01 179107.
1940-05-01 187240.
1940-06-01 185127.
1940-07-01 196333.
1940-08-01 202361.
1940-09-01 190769.
1940-10-01 208026.
1940-11-01 189277.
1940-12-01 189433.
1941-01-01 194228.
1941-02-01 177461.
1941-03-01 202341.
1941-04-01 203080.
1941-05-01 218550.
1941-06-01 220434.
1941-07-01 233565.
1941-08-01 237017.
1941-09-01 231873.
1941-10-01 247137.
1941-11-01 222928.
1941-12-01 232099.
1942-01-01 231251.
1942-02-01 208935.
1942-03-01 237259.
1942-04-01 241688.
1942-05-01 247524.
1942-06-01 252943.
1942-07-01 261215.
1942-08-01 267397.
1942-09-01 262207.
1942-10-01 279252.
1942-11-01 259133.
1942-12-01 273748.
1943-01-01 270158.
1943-02-01 250690.
1943-03-01 284873.
1943-04-01 276156.
1943-05-01 279830.
1943-06-01 284871.
1943-07-01 291091.
1943-08-01 294559.