Within a Project, as soon as you have at least 2 Audits, a ‘Compare Audits’ feature becomes available, under the section ‘Website Audit History.’
This allows you to select any two Audits and compare the data analyzed.
The ‘Compare Audits’ button will initially be dulled out and unclickable – you need to select the two audits you wish to compare by ticking the ‘Compare’ box, at which point you’ll be able to click the button to run the comparison.
This will take you to the Change Report between the two Audits. This contains data from the Reports and Hints sections from one Audit to the next, and shows the change as a percentage increase or decrease.