I make most of mine with Uni 6/0 thread and use a hand held power drill for twisting. I sight down the twisting thread and watch the amount of bow in the line. If it begins to look like a jump rope I add tension, if it looks like a straight line I relax the tension. What I want to see is a slight bow (maybe a half inch) as the thread twists. I am also a "10%er" so I stop twisting when I reach that point. I do think maintaining reasonable tension is important in the final product even for "10%ers".