Protractor
= Protractor
{wiki}
A <protractor> is a graduated instrument for measuring or drawing planar <angles>, commonly a semicircular scale from $0^\circ$ to $180^\circ$. Place its centre at the vertex, align its zero baseline with one ray, and read where the other ray crosses the scale. A $60^\circ$ reading represents $\pi/3$ <radians>. A device with oppositely directed scales requires choosing the scale whose zero matches the aligned baseline.