code: def get_DRAT(delta_x_prime, delta_y_prime, max_ptrm_check):
      
      L = numpy.sqrt(delta_x_prime**2 + delta_y_prime**2)
      DRAT = (old_div(max_ptrm_check, L)) * 100
      return DRAT, L
docs: Input: TRM length of best fit line (delta_x_prime),
          NRM length of best fit line,
          max_ptrm_check
      Output: DRAT (maximum difference produced by a ptrm check normed by best fit line),
          length best fit line