I'll try to explain it the way I read it. Let's say your phone has been on for an hour, and your display has been on for a half hour of that. Your display will show as 50%, since the display has been on for half of the time the phone has been on. The more you are using the phone, the higher the display percentage is going to be. If your phone is only on and being used for 15 minutes out of an hour, the percentage will be much lower. That's how I saw it explained.