To compare results from different instances of a test plan or from different test plans can be very useful to find out variations through time or through configuration. If a test has an instance that can be used as a target, it can be compared with the new results to see if it differs.
To select different set of results for the same test plan, go to the Results table, and click on the PLAN RESULTS. It will display all the results for that specific test plan.
On the new page it will display a table with the results for that specific test plan. On the top left corner, there is a compare icon, as shown in the image below.
When selecting some results (at most 5) and clicking on the Compare icon, a result page is opened with a graph for all the three results and with all the detailed information for each result instance on separate tabs.