'Revision' might be countable or uncountable. I am a little bit confused.
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When revision means a change, it can be countable, as in make a few revisions to a report.
When it means examining something so it can be changed, then it can be both: a system in need of revision AND a revision of standards.
Finally, when it means learning for an exam, it is always uncountable.
Like most derived nouns, revision can refer to a number of things. In the case of revise (the verb that revision is derived from), at least the following senses can be distinguished:
(2) and (3) can be combined: I have all six revisions in my collection.
Only in sense (1) is revision a mass noun; in the other two senses it's a count noun.
Revision may be used plural e.g revisions; but singular form revision may also denote a set of changes. So, at least it is safe to use plural form if you are talking about several sets of "change(s)". E.g:
On the other hand, with the meaning "study" or "review", you may use revision singular as in