code: def get_curve_prime(self):
          
          if len(self.x_Arai_segment) < 4:
              self.pars['specimen_k_prime'], self.pars['specimen_k_prime_sse'] = 0, 0
              return 0
          data = lib_k.AraiCurvature(self.x_Arai_segment, self.y_Arai_segment)
          self.pars['specimen_k_prime'] = data[0]
          self.pars['specimen_k_prime_sse'] = data[3]
docs: not in SPD documentation.  same as k, but using the segment instead of the full data set