Spherical geometry other geometric concepts are defined as in plane geometry, but with straight lines replaced by great circles. Thus, in spherical geometry, angles are defined between great circles, resulting in a spherical trigonometry that differs from ordinary trigonometry in many respects; for example, the sum of the interior angles of a triangle exceeds 180 degrees. Spherical geometry is "not" elliptic geometry, but is rather a "subset" of elliptic geometry. For example, it shares with that geometry the property that a line has no parallels through a given point. Contrast this with Euclidean geometry, in which a line has one parallel through
Protractor traditionally been one-sided. This is thought to be because early manufacturing methods set the tone of future production. Unfortunately, the two number scales on a one-sided protractor often confuse learners when first learning to measure and draw angles. However, in 2009, Jake Adamson, a maths teacher working at Musselburgh Grammar School invented and patented the first two sided protractor trademarked "The Angler". This was a double sided protractor with one scale on each side, avoiding the confusion of having two scales together and enabling easier measuring and drawing of angles. "The Angler" protractor has been widely adopted by schools in