Month	Millions Of Service Hours
1921-07-01	294.700
1921-08-01	321.700
1921-09-01	313.400
1921-10-01	334.700
1921-11-01	313.500
1921-12-01	297.800
1922-01-01	279.000
1922-02-01	258.700
1922-03-01	301.200
1922-04-01	282.000
1922-05-01	305.800
1922-06-01	315.000
1922-07-01	270.600
1922-08-01	313.200
1922-09-01	321.000
1922-10-01	351.800
1922-11-01	340.900
1922-12-01	335.100
1923-01-01	343.800
1923-02-01	307.600
1923-03-01	358.400
1923-04-01	344.200
1923-05-01	366.900
1923-06-01	366.400
1923-07-01	365.900
1923-08-01	383.700
1923-09-01	350.700
1923-10-01	382.300
1923-11-01	345.900
1923-12-01	322.700
1924-01-01	330.000
1924-02-01	310.000
1924-03-01	334.200
1924-04-01	332.500
1924-05-01	337.300
1924-06-01	318.800
1924-07-01	330.000
1924-08-01	333.100
1924-09-01	331.000
1924-10-01	358.100
1924-11-01	319.700
1924-12-01	325.300
1925-01-01	327.500
1925-02-01	295.100
1925-03-01	326.900
1925-04-01	325.300
1925-05-01	327.200
1925-06-01	333.600
1925-07-01	339.800
1925-08-01	339.200
1925-09-01	331.500
1925-10-01	353.900
1925-11-01	322.200
1925-12-01	328.900
1926-01-01	318.600
1926-02-01	296.100
1926-03-01	340.300
1926-04-01	333.500
1926-05-01	336.700
1926-06-01	344.400
1926-07-01	350.000
1926-08-01	351.700
1926-09-01	341.300
1926-10-01	355.800
1926-11-01	336.400
1926-12-01	334.000
1927-01-01	319.300
1927-02-01	291.800
1927-03-01	336.300
1927-04-01	328.100
1927-05-01	334.000
1927-06-01	341.700
1927-07-01	333.200
1927-08-01	346.600
1927-09-01	326.900
1927-10-01	338.600
1927-11-01	313.600
1927-12-01	305.100
1928-01-01	296.200
1928-02-01	281.800
1928-03-01	312.700
1928-04-01	301.200
1928-05-01	324.200
1928-06-01	321.700
1928-07-01	316.900
1928-08-01	333.400
1928-09-01	307.300
1928-10-01	337.900
1928-11-01	306.300
1928-12-01	292.100
1929-01-01	300.400
1929-02-01	272.900
1929-03-01	308.000
1929-04-01	313.100
1929-05-01	326.500
1929-06-01	317.600
1929-07-01	330.800
1929-08-01	339.200
1929-09-01	313.100
1929-10-01	341.200
1929-11-01	303.600
1929-12-01	288.800
1930-01-01	289.800
1930-02-01	259.100
1930-03-01	286.300
1930-04-01	288.900
1930-05-01	294.600
1930-06-01	276.400
1930-07-01	275.500
1930-08-01	271.200
1930-09-01	258.600
1930-10-01	268.600
1930-11-01	233.300
1930-12-01	235.800
1931-01-01	232.900
1931-02-01	207.700
1931-03-01	231.900
1931-04-01	232.100
1931-05-01	230.300
1931-06-01	227.700
1931-07-01	226.900
1931-08-01	218.900
1931-09-01	207.300
1931-10-01	211.000
1931-11-01	183.600
1931-12-01	184.400
1932-01-01	176.800
1932-02-01	169.900
1932-03-01	186.400
1932-04-01	176.700
1932-05-01	174.500
1932-06-01	168.400
1932-07-01	158.100
1932-08-01	161.300
1932-09-01	156.300
1932-10-01	166.300
1932-11-01	157.200
1932-12-01	155.700
1933-01-01	148.100
1933-02-01	134.600
1933-03-01	146.400
1933-04-01	140.600
1933-05-01	152.000
1933-06-01	155.000
1933-07-01	160.800
1933-08-01	173.400
1933-09-01	166.400
1933-10-01	172.700
1933-11-01	158.400
1933-12-01	153.100
1934-01-01	159.800
1934-02-01	147.300
1934-03-01	171.700
1934-04-01	165.400
1934-05-01	178.000
1934-06-01	177.200
1934-07-01	173.600
1934-08-01	177.700
1934-09-01	162.700
1934-10-01	176.300
1934-11-01	158.100
1934-12-01	155.900
1935-01-01	164.500
1935-02-01	149.100
1935-03-01	165.500
1935-04-01	163.200
1935-05-01	169.800
1935-06-01	166.200
1935-07-01	172.100
1935-08-01	174.200
1935-09-01	163.500
1935-10-01	181.300
1935-11-01	164.500
1935-12-01	164.700
1936-01-01	173.100
1936-02-01	172.500
1936-03-01	180.800
1936-04-01	182.900
1936-05-01	184.000
1936-06-01	187.900
1936-07-01	193.300
1936-08-01	192.200
1936-09-01	191.400
1936-10-01	204.600
1936-11-01	185.300
1936-12-01	194.100
1937-01-01	187.300
1937-02-01	178.100
1937-03-01	205.000
1937-04-01	202.400
1937-05-01	204.600
1937-06-01	210.100
1937-07-01	211.100
1937-08-01	207.700
1937-09-01	196.800
1937-10-01	199.300
1937-11-01	179.500
1937-12-01	173.800
1938-01-01	162.100
1938-02-01	146.100
1938-03-01	165.100
1938-04-01	154.400
1938-05-01	153.200
1938-06-01	157.200
1938-07-01	157.800
1938-08-01	169.100
1938-09-01	165.500
1938-10-01	174.600
1938-11-01	164.800
1938-12-01	165.900
1939-01-01	162.400
1939-02-01	150.300
1939-03-01	173.400
1939-04-01	161.000
1939-05-01	171.300
1939-06-01	176.400
1939-07-01	173.800
1939-08-01	184.000
1939-09-01	179.000
1939-10-01	194.800
1939-11-01	182.500
1939-12-01	175.300
1940-01-01	179.400
1940-02-01	165.200
1940-03-01	175.300
1940-04-01	174.600
1940-05-01	182.200
1940-06-01	179.900
1940-07-01	190.600
1940-08-01	196.200
1940-09-01	184.100
1940-10-01	201.700
1940-11-01	182.800
1940-12-01	182.400
1941-01-01	187.000
1941-02-01	170.800
1941-03-01	194.600
1941-04-01	196.800
1941-05-01	210.700
1941-06-01	211.500
1941-07-01	223.900
1941-08-01	227.000
1941-09-01	221.600
1941-10-01	236.600
1941-11-01	213.300
1941-12-01	222.100
1942-01-01	220.400
1942-02-01	198.900
1942-03-01	226.500
1942-04-01	231.200
1942-05-01	235.000
1942-06-01	240.800
1942-07-01	246.600
1942-08-01	251.100
1942-09-01	243.800
1942-10-01	259.400
1942-11-01	238.900
1942-12-01	251.700
1943-01-01	246.600
1943-02-01	228.400
1943-03-01	261.000
1943-04-01	253.600
1943-05-01	252.600
1943-06-01	258.400
1943-07-01	261.700
1943-08-01	263.600