Topic summary
Angle measure
Extracted from the Wikipedia article Angle.
Measuring angles
Angle measurement encompasses both direct physical measurement using a measuring instrument such as a protractor, as well as the theoretical calculation of angle size from other known quantities. While the measurement of angles is intrinsically linked with rotation and circles, there are various perspectives as to exactly what is being measured, including amongst others: the amount of rotation about the vertex of one ray to the other; the amount of opening between the rays; or the length of the arc that subtends the angle at the centre of a unit circle.