private static double GetNextSlope(int index, int count, List <DateValue> values, DateValue dv)
        {
            double nextSlope = 0;

            if (index < count - 1)
            {
                DateValue dv2 = values[index + 1];
                nextSlope = (dv2.Value - dv.Value) / (dv2.Date.ToOADate() - dv.Date.ToOADate());
            }
            return(nextSlope);
        }