Lets use tonight's game between Utah and Oklahoma City as an example:
Utah's PR = 102.7
Oklahoma City's PR = 92.3
Line = -5.5
Subtract the lesser PR from the greater one : 102.7-92.3 = 10.40
Add the line to this : 10.40+(-5.5) = 4.90
Since this number is great than 2, it is a play. If you were to go through this method, and you get a value less than -2, then you play the other team ATS.