By turning a line of sight exactly 90 degrees, the angle prism provides an easily plotted relationship between survey points. It is an inexpensive hand-held instrument which requires no adjustment and may be used to advantage in many types of geologic mapping.The instrument is particularly useful in constructing grid maps and underground stope maps. It may also be used in finding distances to inaccessible objects, in providing secondary control for plane table surveys, and in checking completed maps against gross error. A rapid triangulation net can be constructed with the prism and plotted on coordinate paper.

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