The general plan of extending the first‐order level net of the United States has been to locate the lines in such a way that eventually no place in the country will be more than fifty miles from a standard bench mark.In prosecution of this plan, 50,000 miles of first‐order levels have been run by the U.S. Coast and Geodetic Survey, the U.S. Geological Survey, the Corps of Engineers, U.S. Army, the U.S. Lake Survey, the Mississippi and Missouri River Commissions, and a number of the leading railroads. The work enters every State of the union but one—Delaware— and forms over one hundred c