 The curvature of a surface at a point \(p\) on the surface measures how much the surface bends away from its tangent plane at \(p\). The curvature of a surface is constant if at every point \(p\) of the surface the surface bends away from the tangent plane by the same quantity. Examples of surfaces which can be used to model various geometries are the surface of the cylinder (Euclidean; constant curvature 0), the sphere (spherical; positive curvature), and the horse saddle (hyperbolic; negative curvature). They are all homogenous and isotropic but they have different constant curvature.