Angle ∠BAC might refer to any of four angles: the clockwise angle from B to C, the anticlockwise angle from B to C, the clockwise angle from C to B, or the anticlockwise angle from C to B, where the direction in which the angle is measured determines its sign (see Positive and negative angles). However, in many geometrical situations it is obvious from context that the positive angle less than or equal to 180 degrees is meant, and no ambiguity arises. Otherwise, a convention may be adopted so that ∠BAC always refers to the anticlockwise (positive) angle from B to
Angle C, and ∠CAB to the anticlockwise (positive) angle from C to B. The names, intervals, and measured units are shown in a table below: When two straight lines intersect at a point, four angles are formed. Pairwise these angles are named according to their location relative to each other. A transversal is a line that intersects a pair of (often parallel) lines and is associated with "alternate interior angles", "corresponding angles", "interior angles", and "exterior angles". There are three special angle pairs which involve the summation of angles: The size of a geometric angle is usually characterized by the magnitude