Dragon Age 2: Okay, So, exactly how much is 50% rivarly/friendship points?

I'm a little fuzzy on just how much this is- Is it when the companion bar is maxed to one end or the other? Or is when you guestamate that it's 50% towards the rival/friendship? I'm a bit confusion, or maybe I'm over thinking/ being too cautious. Better safe than sorry? I rather not trust myself and be wrong and waste aaaaaaall this time.