Pick MAX of a list of dates in one table to update LatestDate in another

[cheserex]

I have a database of documents- each document has a docID. I have another table listing revisions with dates, revisor, etc.
I would like to find a way to automatically update LastRevDate in the documents tablewith the Latest (Max) date in the Revisions table


I've tried a query with an aggregate of [revisiondate] and can get as far as listing documents that do not meet [Lastrevdate]<>MaxofRevisiondate, but cannot update based on this.
I have an entry form with Documents table and a subform showing the revision dates list from the Revisions table. Ideally I want to create an event that will automatically find the Max([revisiondate] and replace the [LastRevDate] in the documents table based on the common [docID]

[June7]

Why even have this field? Maintaining calculated data (data dependent on other data) is usually a bad idea. The data can get out of sync.

If it can be calculated for an UPDATE action it can be calculated whenever needed. Could use DMax function. Or maybe a nested subquery, review http://allenbrowne.com/subquery-01.html