Lately I'm of the opinion that it's the father's line that really matters. So for a man, it's basically a binary test if his entire paternal lineage is white. For the many branches on the women's side I think there is room for leniency. I think a scientific basis could be made, but an easier way if you ever meet any mutts is to pay attention to how your gut instinct feels if someone is mixed with nigger on their mom's side or their dad's. It actually feels different, like that's where the racial essence is. Which also kind of explains how women can so easily be disinterested in preserving the race. Women are maybe more of a way to pull genetic strengths or problems into a race - a desirable woman pulling in health, fertility, beauty, and the benefits of being nurtured well in early childhood, and an undesirable woman counting as a loss of those things in your branch of descendants. It's obviously not just that simple but as a general framework I think it holds up pretty well.