Protractor the UK. Protractor A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into arcminutes. They are used for a variety of mechanical and engineering-related applications. One common use is in geometry lessons in schools. Some protractors are simple half-discs. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. A bevel protractor is
Ovoid (projective geometry) lines which have 3 points in common with the set and the lines are not contained in the set. Examples of semi-ovoids are the sets of isotropic points of an hermitian form. They are called "hermitian quadrics". As for ovoids in literature there are criteria, which make a semi-ovoid to a hermitian quadric. See, for example. Semi-ovoids are used in the construction of examples of Möbius geometries. Ovoid (projective geometry) In projective geometry an ovoid is a sphere like pointset (surface) in a projective space of dimension . Simple examples in a real projective space are hyperspheres (quadrics). The essential