curvature of a surface

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curvature of a surface 

A measure of the shape of a curved surface. It is expressed in a unit called reciprocal metre, usually written as m−1, which is equal to the reciprocal of the radius of curvature of a surface in metres. Example: if a surface has a radius of curvature r of +0.5 m, its curvature R will be R = 1/r = 1/+0.5 = 2 m−1.