All the articles (formula) are useful for calculating the approximate value of solid angle subtended by a circular plane at any point in the space. These are also applicable for calculating all the parameters such as major axis, minor axis & eccentricity of elliptical plane of projection of a circular plane when viewed from any off-center position in the space. All the articles have been derived by the author using Approximation Formula of Solid Angle for Symmetrical Planes which had been derived by the author in his book “Advanced Geometry”.