Each man in the company can be used as a sentinel or as a watcher, but not all as observers. To become an observer, a man must have a special capacity for this task. Each platoon should have at least six such observers of proper qualification; good eyesight and hearing, patient, and a good shot. They are relieved every two hours. Observation duty is carried out in daylight. The observers are of two kinds: (1) In each company the platoon observers are distributed in a number of observation posts especially chosen for this purpose. These posts are located in the support point of the company which may be in advance of the firing line, in the firing line, or in any point within the position that has a wide view of the front. These observers employ periscopes or field glasses. Everything of note that is observed is recorded and from this data the captain makes out his daily observation report. (2) Also, in the sector, there are special observatories belonging to the headquarters of the regiment, under the command of the intelligence officer of the sector. There are usually two or three observatories, from which the information is transmitted directly to the colonel. These observatories are furnished with field glasses, maps, and telephones. In general, all observers are required to obtain all possible information of the enemy, to record all modifications of the hostile position in its works and wire entanglements, all the movements that they can observe, all working parties that they can discover. Also, they receive special orders for the cases they must report to the commander, as for instance: shelling of the position by artillery or trench mortars, gas attacks, signal rockets fired in the front line, activities of the aviation services, whether of friend or enemy. CHAPTER IV THE RELIEF I. Definitions and Principles There are two kinds of reliefs, General and Interior reliefs. A =General Relief= is one where a large unit, such as a division or an army corps, is relieved from its position on the front. An =Interior Relief= is one where a small unit, such as a company, battalion, or regiment, is relieved from its area by another unit of the same division within the position. A general relief takes place for the following reasons: In order to send a unit far to the rear to good billets for complete rest and perhaps for recruiting. To withdraw and gather together the units of a corps, for the purpose of training for an offensive. To permit the strategical movement of large units along the entire front. [Illustration: _Interior Relief in the Division_]