Surveyors label the three parts of an angle as the backsight (base line), the vertex and the foresight. Angles can be measured or laid out using instruments, direct method, or by measuring, indirect method. There are three common indirect methods for measuring or laying out an angle. Two of these are limited to 90° angles, the chord method and the 3-4-5 method, the third, tape sine, can be used with any angle between 0° and 90°. The following discussion illustrates all three methods.
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