This is a look behind the scene to show how the revision number is calculated.
Subversion
The SCM revision for subversion is determined by retrieving the changelog for the project for the last day specified by the queryRangeInDays property. If no changes have been found, the period will be incremented by the query range amount up to five times. If no changes have been found within the (set per default) 150 days, the SCM revision number will not be retrieved.