Month	Millions Of Hours
1921-07-01	3.30000
1921-08-01	3.18000
1921-09-01	3.04000
1921-10-01	3.07000
1921-11-01	2.97000
1921-12-01	3.06000
1922-01-01	3.04000
1922-02-01	2.80000
1922-03-01	3.08000
1922-04-01	2.96000
1922-05-01	3.09000
1922-06-01	3.13000
1922-07-01	3.06000
1922-08-01	2.92000
1922-09-01	2.74000
1922-10-01	2.80000
1922-11-01	2.73000
1922-12-01	2.84000
1923-01-01	2.95000
1923-02-01	2.70000
1923-03-01	2.99000
1923-04-01	2.94000
1923-05-01	3.12000
1923-06-01	3.08000
1923-07-01	3.28000
1923-08-01	3.29000
1923-09-01	3.14000
1923-10-01	3.15000
1923-11-01	3.03000
1923-12-01	3.15000
1924-01-01	3.10000
1924-02-01	2.92000
1924-03-01	3.14000
1924-04-01	3.08000
1924-05-01	3.22000
1924-06-01	3.22000
1924-07-01	3.37000
1924-08-01	3.36000
1924-09-01	3.20000
1924-10-01	3.19000
1924-11-01	3.09000
1924-12-01	3.18000
1925-01-01	3.22000
1925-02-01	2.97000
1925-03-01	3.28000
1925-04-01	3.23000
1925-05-01	3.32000
1925-06-01	3.33000
1925-07-01	3.49000
1925-08-01	3.51000
1925-09-01	3.33000
1925-10-01	3.35000
1925-11-01	3.24000
1925-12-01	3.38000
1926-01-01	3.47000
1926-02-01	3.19000
1926-03-01	3.50000
1926-04-01	3.44000
1926-05-01	3.59000
1926-06-01	3.58000
1926-07-01	3.73000
1926-08-01	3.70000
1926-09-01	3.58000
1926-10-01	3.56000
1926-11-01	3.46000
1926-12-01	3.60000
1927-01-01	3.64000
1927-02-01	3.35000
1927-03-01	3.62000
1927-04-01	3.48000
1927-05-01	3.59000
1927-06-01	3.59000
1927-07-01	3.76000
1927-08-01	3.75000
1927-09-01	3.58000
1927-10-01	3.54000
1927-11-01	3.43000
1927-12-01	3.54000
1928-01-01	3.60000
1928-02-01	3.38000
1928-03-01	3.57000
1928-04-01	3.45000
1928-05-01	3.60000
1928-06-01	3.57000
1928-07-01	3.58000
1928-08-01	3.70000
1928-09-01	3.53000
1928-10-01	3.55000
1928-11-01	3.40000
1928-12-01	3.58000
1929-01-01	3.59000
1929-02-01	3.28000
1929-03-01	3.61000
1929-04-01	3.50000
1929-05-01	3.64000
1929-06-01	3.65000
1929-07-01	3.87000
1929-08-01	3.87000
1929-09-01	3.67000
1929-10-01	3.68000
1929-11-01	3.54000
1929-12-01	3.69000
1930-01-01	3.75000
1930-02-01	3.45000
1930-03-01	3.76000
1930-04-01	3.62000
1930-05-01	3.69000
1930-06-01	3.66000
1930-07-01	3.79000
1930-08-01	3.77000
1930-09-01	3.52000
1930-10-01	3.50000
1930-11-01	3.36000
1930-12-01	3.58000
1931-01-01	3.55000
1931-02-01	3.25000
1931-03-01	3.51000
1931-04-01	3.36000
1931-05-01	3.43000
1931-06-01	3.30000
1931-07-01	3.44000
1931-08-01	3.39000
1931-09-01	3.22000
1931-10-01	3.18000
1931-11-01	3.05000
1931-12-01	3.18000
1932-01-01	3.14000
1932-02-01	2.92000
1932-03-01	3.05000
1932-04-01	2.93000
1932-05-01	2.98000
1932-06-01	2.86000
1932-07-01	2.94000
1932-08-01	2.88000
1932-09-01	2.72000
1932-10-01	2.73000
1932-11-01	2.66000
1932-12-01	2.78000
1933-01-01	2.74000
1933-02-01	2.48000
1933-03-01	2.68000
1933-04-01	2.55000
1933-05-01	2.65000
1933-06-01	2.67000
1933-07-01	2.76000
1933-08-01	2.77000
1933-09-01	2.73000
1933-10-01	2.79000
1933-11-01	2.60000
1933-12-01	2.76000
1934-01-01	2.75000
1934-02-01	2.52000
1934-03-01	2.75000
1934-04-01	2.68000
1934-05-01	2.79000
1934-06-01	2.75000
1934-07-01	2.90000
1934-08-01	2.91000
1934-09-01	2.80000
1934-10-01	2.82000
1934-11-01	2.67000
1934-12-01	2.87000
1935-01-01	2.91000
1935-02-01	2.62000
1935-03-01	2.87000
1935-04-01	2.77000
1935-05-01	2.88000
1935-06-01	2.84000
1935-07-01	2.97000
1935-08-01	2.99000
1935-09-01	2.84000
1935-10-01	2.90000
1935-11-01	2.78000
1935-12-01	3.04000
1936-01-01	3.06000
1936-02-01	2.83000
1936-03-01	2.97000
1936-04-01	2.93000
1936-05-01	3.01000
1936-06-01	3.01000
1936-07-01	3.20000
1936-08-01	3.19000
1936-09-01	3.08000
1936-10-01	3.14000
1936-11-01	3.03000
1936-12-01	3.39000
1937-01-01	3.31000
1937-02-01	2.99000
1937-03-01	3.32000
1937-04-01	3.19000
1937-05-01	3.23000
1937-06-01	3.24000
1937-07-01	3.40000
1937-08-01	3.46000
1937-09-01	3.25000
1937-10-01	3.24000
1937-11-01	3.08000
1937-12-01	3.34000
1938-01-01	3.29000
1938-02-01	2.95000
1938-03-01	3.19000
1938-04-01	3.08000
1938-05-01	3.07000
1938-06-01	3.07000
1938-07-01	3.21000
1938-08-01	3.17000
1938-09-01	3.04000
1938-10-01	3.03000
1938-11-01	2.96000
1938-12-01	3.27000
1939-01-01	3.22000
1939-02-01	2.90000
1939-03-01	3.22000
1939-04-01	3.06000
1939-05-01	3.15000
1939-06-01	3.14000
1939-07-01	3.36000
1939-08-01	3.33000
1939-09-01	3.16000
1939-10-01	3.16000
1939-11-01	3.01000
1939-12-01	3.33000
1940-01-01	3.29000
1940-02-01	3.04000
1940-03-01	3.26000
1940-04-01	3.13000
1940-05-01	3.14000
1940-06-01	3.16000