The angle between a line and the prolongation of the preceding line is called a deflection angle. Deflection angle can also be used to note the direction of a line. It is recorded as right or left depending on whether the line to which measurement is taken lies to the right (clockwise) or left (counterclockwise) of the prolongation of the preceding line. Figure 19.11 shows deflection angles. In this, the line BC is having a right deflection angle CD does have left deflestion angle. Deflection angles may have values between 0° and 180°, but usually they are not employed for angles greater than 90°. In any closed polygon the algebraic sum of the deflection angles (considering right deflections as of sign opposite to left deflections) is 360°.

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