Wrong...as I pointed out this procedure tells us very much about a person’s mass, specifically how much mass they have in regards to muscle mass vs. fat mass/body fat.
It appears your research is incomplete or your logic is faulty, but that’s why they dunk people in the tank...to find out how fat they are, they could care less about their volume.
Nice try, but we aren't talking about motives and goals. We are talking about what is measured by immersion.
It's really amusing to watch you people squirm.
Read a full description of what is done in the calculation of body fat. You need to calculate density, which is a ratio of volume to weight (or mass if you insist).
Immersion measures body volume.