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
Perceived visual angle specifies the amount by which one should rotate one's eye to quickly look from one seen point to another eye tracking, saccade, observers in other experiments shifted their gaze from one object endpoint to the other, and the angle the eye rotated through was measured as "θ′" for that object (Yarbus (1967). It is important to understand how "θ′" differs from "S′". Consider an example illustrated by the sketch at the right. Suppose one is looking through a window at a house 240 feet away, so it subtends a visual angle of about 7 degrees. The window opening is 10