| Coded variable level | Unit | symbol | variable | ||
| High | Center | Low | |||
| 5 | 3 | 1 | Kg/M3 | A | Thiourea |
| 3 | 2 | 1 | Kg/M3 | B | Fe2(SO4)3 |
| 60 | 45 | 30 | ˚C | C | Temperature |
| 75 | 60 | 45 | μm | D | Size |