In addition to the knife, oxygen, vision mask, and flippers, some missions require other devices to assure the success of the project and the safe return of the man himself. Some missions, such as mapping projects, require too that accurate knowledge of the bottom, direction of currents, and depths encountered, be recorded. This knowledge is obtained partly from past experience but mainly from small, compact, accurate instruments carried by the Frogmen. Here we see a warm-water swimmer about to start his project, so equipped. On his right wrist he wears an accurate magnetic compass that can be read easily under water. On his left wrist he wears, first, the conventional waterproof wrist watch next to his hand and then above it up his arm an accurate depth gauge to tell him just how far below the surface he is. These three, plus visual observation, will enable him to make a quite accurate map of his underwater terrain. Hanging about his neck is a sheet of plastic and a sharp-pointed stylus. With the latter , notes can be made upon the plastic sheet (in place of paper and pencil), from which to make the accurate map later on.
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