After putting a little thought into it, you can tell if the bearings are showing the "weak side/s" of the spine OR the curve of the arrow (all arrows have SOME curve...even if it's only .001"
find the weak side of the arrow using the bearing test.
Now turn the arrow 180 degrees. and retry the test. if the arrow moves, you have found the curve. if not, you have found the weak side (better word might be plane) of the arrow.
each arrow I have tested (cx 3-d selects) have shown the bearing test to show the "weak side of the spine" to be the curve of the arrow. Even on arrows at LESS than .001" I was not able to find an arrow that showed a weak spine on any side that would show up on the other side (180 degrees).
Again, this was only with cx carbon arrows...others may be different.