Abbreviations and codes used in the observer's diary
Table 4: Code for observing and reporting visibility (download PDF version)
| CODE | General Description | Visibility Range (inclusive) | Standard Distance | ||
| yards | metres | yards | metres | ||
| X | DENSE FOG | 0 - 24 | 0 - 19 | ||
| E | 25 - 44 | 20 - 39 | 22 | 20 | |
| 0 | THICK FOG | 45 - 104 | 40 - 99 | 44 | 40 |
| 1 | 105 - 210 | 100 - 199 | 110 | 100 | |
| 2 | FOG | 220 - 430 | 200 - 399 | 220 | 200 |
| 3 | MODERATE FOG | 440 - 1090 | 400 - 999 | 440 | 400 |
| FOG LIMIT | |||||
| 4 | VERY POOR VISIBILITY | 1100 - 2190 | 1000 - 1999 | 1100 | 1000 |
| 5 | POOR VISIBILITY | 2200 - 4390 | 2000 - 3999 | 2200 | 2000 |
| miles | km | miles | km | ||
| 6 | MODERATE VISIBILITY | 2½ | 4 | ||
| 3 - 6 | 4 - 9 | 4⅓ | 7 | ||
| 7 | GOOD VISIBILITY | 7 - 12 | 10 - 19 | 6¼ | 10 |
| 8 | VERY GOOD VISIBILITY | 12½ | 20 | ||
| 13 - 24 | 20 - 39 | 18⅔ | 30 | ||
| 9 | EXCELLENT VISIBILITY | 25 or over | 40 or over | 25 | 40 |
