That's why I always spin my prop on both cones and re-check balance to make sure I'm not seeing this effect.
ORIGINAL: ZAGNUT
problem with most balancers i've seen is the way the prop is supposed to be centered with those stupid cones. all it takes is a slight imperfection on the very edge of the prop hub's hole for the cones to hold the prop way off center! when clamped right it is amazing how close to perfect balance APC props are...but put them on the cones and they suddenly need lead added to one side of the hub...
dave