MissionPlanner.MagCalib.sphere_error C# (CSharp) Method

        static void sphere_error(double[] xi, double[] fi, object obj)
        {
            double xofs = xi[0];
            double yofs = xi[1];
            double zofs = xi[2];
            double r = xi[3];
            int a = 0;
            foreach (var d in (List<Tuple<float, float, float>>) obj)
            {
                double x = d.Item1;
                double y = d.Item2;
                double z = d.Item3;
                double err = r - Math.Sqrt(Math.Pow((x + xofs), 2) + Math.Pow((y + yofs), 2) + Math.Pow((z + zofs), 2));
                fi[a] = err;
                a++;
            }
        }