A Baseline scan is a scan that you save as a reference for a comparison with another scan. You compare scans when you generate a Historical Comparison report. Unlike a Previous scan, which gets replaced as a new Current scan is created, a Baseline scan is retained indefinitely until you decide to delete it. You can have only one Baseline scan per scan target.
IMPORTANT:Because you can have only one Baseline scan per scan type for a scan target, establishing a scan as a Baseline will override any established Baseline scan of the same scan type for the same scan target.
Select Scans > Scan Data.
In the far left column, select the check box pertaining to the scan you want to set as a Baseline scan.
Click Set Baseline.
When the confirmation dialog box appears, click Yes.