The biblatex manual describes the number field as
The number of a journal or the volume/number of a book in a series. See also issue as well as §§ 2.3.7, 2.3.10, 2.3.11. With @patent entries, this is the number or record token of a patent or patent request.
The meaning for journal articles and patents makes sense to me. However, the number field applies to a number of other entries according to that manual. Specifically, all of the following:
| entry | description |
|---------------+-----------------------|
| article | Journal issue number. |
| book | |
| mvbook | |
| inbook | |
| collection | |
| mvcollection | |
| incollection | |
| dataset | |
| manual | |
| patent | Patent number. |
| periodical | |
| proceedings | |
| mvproceedings | |
| inproceedings | |
| report | |
For a book, how does number differ from volume? From the description, it sounds like they mean the same thing in this context. If so, why not just use volume?
What is the meaning for a manual entry? I'm citing a manual for some electronic equipment that declares a part number ("HP Document Part Number 03458-90033"). Would "03458-90033" be a correct usage of the number field in this context?
Finally, reports are often identified with a numeric identifier. And, frequently this just counts up from 1 where 1 is the first report published by the organization (e.g., application note 98). I presume this is what is meant by number in the context of a report. Is that correct?