Ok Understood,
Ok I guess that explains my "nice" comb from the cache and my jagged flip/flop . sometimes zero comb from the "full" matrix normal ...
I also have different tangents from manually "calculating" them then v3, v2. But I will make a "sanity" check this weekend (feed manual matrixes into my code instead of spline "point" matrixes), before I post about this.
Thanks Ferdinand
I'll divide and conquer away.