| Sign | pH amount | Description |
| Ao | <8 | Without alkalinity limitation |
| A1 | 8 - 8.5 | Low alkalinity limitation |
| A2 | 8.5 - 9 | Relatively high alkalinity limitation |
| A3 | 9 - 9.5 | High alkalinity limitation |
| A4 | >9.5 | Very high alkalinity limitation |