code: def get_DRATS(sum_ptrm_checks, sum_abs_ptrm_checks, x_Arai, end):
      
      DRATS = (old_div(sum_ptrm_checks, x_Arai[end])) * 100.
      DRATS_prime = (old_div(sum_abs_ptrm_checks, x_Arai[end])) * 100.
      return DRATS, DRATS_prime
docs: input: sum of ptrm check diffs, sum of absolute value of ptrm check diffs,
          x_Arai set of points, end.
      output: DRATS (uses sum of diffs), DRATS_prime (uses sum of absolute diffs)