They address this in the paper, but from the opposite angle (ho):

  It should be noted that our dipping scheme assumes that the
  object has no vertical _caps_ in any orientation. A cap is a vertical
  cavity that forms a vessel, in which water can be accumulated if
  the object is elevated vertically and air can be trapped, generating
  air pockets when the object is dipped in the opposite orientation.
  Most caps, if they exist, would be small and would have a minor
  effect akin to noise on the dip transform. Nevertheless, caps can be
  detected by dipping and then lifting back the object with the liquid
  trapped in the cap, yielding two different water levels. Flipping the
  object vertically allows detecting air pockets as they become caps.

Mobile friendly:

> It should be noted that our dipping scheme assumes that the object has no vertical _caps_ in any orientation. A cap is a vertical cavity that forms a vessel, in which water can be accumulated if the object is elevated vertically and air can be trapped, generating air pockets when the object is dipped in the opposite orientation. Most caps, if they exist, would be small and would have a minor effect akin to noise on the dip transform. Nevertheless, caps can be detected by dipping and then lifting back the object with the liquid trapped in the cap, yielding two different water levels. Flipping the object vertically allows detecting air pockets as they become caps.

Thanks, I forget that quoted text is horrible on HN on mobile.

You're not quoting text, you're formatting it as code. Just put "> " instead of indenting.

aren't there some pretty basic CSS rules to even make the formatted code look better on a narrow screen mobile? something like `white-space: pre-wrap`, IIRC?

maybe I should look into how to add custom CSS rules to a particular site (HN), can you do that native in firefox, or does it need a plugin?

By dipping from various different angles

It's a bit like a fluid pet scan, each angle will give partial information, you "integrate" to gather the surface.

Gives me ideas.

Think of the intro to the Ghost in the Shell, where the android body is floating up through a bath, and the manufacturer layer on the body is dissolving and being removed. This method could detect that the material is 100% removed from the body as well as confirm that the body is created exactly to spec.

I guess that would be possible, but one has to do some trickery to find false data.

Maybe correlating the exact oposite dip works: Dipping a bowl shows a negative volume then the bowl begins to fill. A dome (reversed bowl) will show additional volume of trapped air at the same point.