Grinding wheel balancing fixture - video

[Toolmaker51]

Both posts have good details, using otherwise too large parallels is clever, not to mention already heat treated and ground.
I too, prefer a bit more responsive bubble level. That would allow 3 leveling 'feet', while just two are operated to correct the adjustments [figuratively pitch & yaw].
But any leveler I've used [or seen] had an arbor shaped axle, not loose per the video. It's clearly sufficient, demonstrating lots of settling time. I believe any decent size drill blank or reamer shank offers all the straightness and little rolling resistance to be a logical choice.
Planer blades! How come I don't know any woodworkers?

[edit 21 Aug]
The arbor question kept recurring. All I can figure is those were larger wheels; a bushing could be right size but imperfect perpendicularity to wheel edge. That 'nodding' would be tough to balance out of plane, let alone wheel itself.
Still interested regarding the plain shaft, certain that largest slip fit diameter is satisfactory.

Bullseye level offered by mwmkravchenko is quite nice at 1° range in .002 increments.