| Rating | Criteria |
|---|---|
| 10 | No attack; 1 to 2 small nibbles permitted |
| 9 | Nibbles to 3% of cross-section |
| 8 | Penetration of from 3% to 10% of cross-section |
| 7 | Penetration of from 10% to 30% of cross-section |
| 6 | Penetration of from 30% to 50% of cross-section |
| 4 | Penetration of from 50% to 75% of cross-section |
| 0 | Failure |