| Independent variable | Axial −α | Min −1 | CP 0 | Max +1 | Axial α |
| Nitrogen (mg·L−1) | 0.0 | 42.5 | 106.2 | 170.0 | 212.5 |
| Phosphorus (mg·L−1) | 0.0 | 13.2 | 33.1 | 53.0 | 66.2 |
| Vitamin (mg·L−1) | 0.0 | 0.13 | 0.32 | 0.50 | 0.63 |