Original issue, US Army Technical Manual, 137 pages, size is 8 1/4" x 10 3/4", stapled, three hole punched, dated 27 September 1979.  This is not a commercial copy or print but an original issue government print issued in 1979 and republished in 1983 to include changes 1 through 10.  This publication is titled - TM 55-1660-245-13, Maintenance Instructions for Oxygen Equipment.  This publication provides informtion and instructions for the repair and maintenance requirments and procedures of aviation oxygen equipment.  Very well illustrated using photographs and detailed and clear line drawings.