19. The designations _line of platoons_, _line of companies_, _line of battalions_, etc., refer to the formations in which the platoons, companies, battalions, etc., each in column of squads, are in line. 20. Full distance in column of subdivisions is such that in forming line to the right or left the subdivisions will have their proper intervals. In column of subdivisions the guide of the leading subdivision is charged with the step and direction; the guides in rear preserve the trace, step, and distance. 21. In close order, all details, detachments, and other bodies of troops are habitually formed in double rank. To insure uniformity of interval between files when falling in and in alignments, each man places the palm of the left hand upon the hip, fingers pointing downward. In the first case the hand is dropped by the side when the next man on the left has his interval; in the second case, at the command _front_. 22. The posts of officers, noncommissioned officers, special units (such as band or machine-gun company), etc., in the various formations of the company, battalion, or regiment, are shown in plates. In all changes from one formation to another involving a change of post on the part of any of these, posts are promptly taken by the most convenient route as soon as practicable after the command of execution for the movement; officers and noncommissioned officers who have prescribed duties in connection with the movement ordered, take their new posts when such duties are completed. As instructors, officers and noncommissioned officers go wherever their presence is necessary. As file closers it is their duty to rectify mistakes and insure steadiness and promptness in the ranks. 23. Except at ceremonies, the special units have no fixed places. They take places as directed; in the absence of directions, they conform as nearly as practicable to the plates, and in subsequent movements maintain their relative positions with respect to the flank or end of the command on which they were originally posted. 24. General, field, and staff officers are habitually mounted. The staff of an officer forms in single rank 3 paces in rear of him, the right of the rank extending 1 pace to the right of a point directly in rear of him. Members of the staff are arranged in order from right to left as follows: General staff officers, adjutant, aids, other staff officers, arranged in each classification in order of rank, the senior on the right. The flag of the general officer and the orderlies are 3 paces in rear of the staff, the flag on the right. When necessary to reduce the front of the staff and orderlies, each line executes _twos right_ or _fours right_, as explained in the Cavalry Drill Regulations, and follows the commander. When not otherwise prescribed, staff officers draw and return saber with their chief. 25. In making the about, an officer, mounted, habitually turns to the left.