Can anybody tell me how Civil calculates the percentage of Slopes?Thank you very much!

Civil 3d calclulates triangles.These triangles have a specific and only one slope.So when civil 3d returns the slope, in fanct returns the slope of each triangle.In fact the slope of each triangle is a slope of a "straight furface", coming from the 3 points of the triangle.I hope i helped you 

Are asking about the specifi formula Civil 3D uses ? If so, Civil 3D creates surfaces using the Delaunay triangulation method. from there slopes are derived use the triangles as described by nkiakasC. ChambersInfratech Civilhttps://infratechcivil.com