Symptom
In the approval workflow variable "compare revisions" stores a link with that you are redirected to the model comparator in SPM. In the left panel you have an older revision and in the right panel the newer. It would be important to know under what conditions the revisions have been picked for the approval, because sometimes are compared the last with before last, and another time the first with the before last.
Resolution
The more recent (i.e. higher number) revision is the one for which the approval workflow was started.
The older (i.e. lower number) revision is the most recent revision (based on the given revision), which also went through an approval. In case there is no such revision, the first revision is returned.
Keywords
approval workflow, swa, spg, spm, Process Manager, Process Governance, revision, comparator, compare revisions , KBA , BPI-SIG-HUB-DC , Diagram Comparator for SAP Signavio , Problem