You have to pull the axle out of the tube and check it somehow. I used a drywall square. There is a max. runout spec in the book, but, since it was bad enough for me to see just by eyeballing it, i did not bother to set that up and measure.

You might remember my post about bent axles - I still never figured out why this happens. It must not be a "rare" thing since one of the junkyard axles I looked at was bent too.