Module 3 - Phonetic Alphabet & Prowords
Numbers and Critical Digits
The modified forms are an aid to intelligibility, not a licence to change the number. Work from the written value, speak one digit at a time and keep the original order. A nine-digit MMSI must remain nine digits from the first group to the last.
IMO also prints TOUSAND for 1000. For 2.5, its numbers section shows both two decimal five and two point five. This module uses decimal in drills because it is distinctive, while recognising the other documented form.
Pair every number with its meaning. One-six might be a channel, but the receiver should not have to infer that. State Channel one-six, bearing one-three-seven degrees or distance two decimal four nautical miles as appropriate.
| Number | IMO pronunciation | Number | IMO pronunciation |
|---|---|---|---|
| 0 | ZEERO | 5 | FIFE |
| 1 | WUN | 6 | SIX |
| 2 | TOO | 7 | SEVEN |
| 3 | TREE | 8 | AIT |
| 4 | FOWER | 9 | NINER |
| 1000 | TOUSAND | 2.5 | TOO DECIMAL FIFE or TOO POINT FIFE |
Optional quick check
Section 5 of 7
How is 150 normally spoken under the IMO separate-digit rule?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Phonetic Alphabet & Prowords
This public lesson is part of Revision Module 3. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.