OK, so why not take a screen shot of your full polar diagram for reference, then re-set it each day to compare with the saved screen shot?
You should remember that the polar diagram is only produced when you pick up an aircraft, so a polar diagram produced during the day is going to be very different to one produced overnight, so it's not necessarily a good indication of how your system is working. Same will apply when you compare one day to another, as traffic will vary