Is it within your mental capacity to undestand that displacement provides a measurement of volume, and when put in a formula along with weight, provides density?
Is it within your mental capacity to recall your first question about measuring a person’s mass?
They don’t dunk people in tanks just for the fun of finding out anything about vloume but how fat they are. Fat MASS...as a percentage of body WEIGHT.
Conversely, if the issue was only weight, they’d merely weigh a person and be done with it.
The two are taken together to determine a person’s percentage of body fat, or fat MASS, and this is a way of determing it, and body fat MASS is ultimately determined in number of pounds, or kilos, not volume.
It’s just that we can’t cut a person up and separately weigh their muscles and then weigh their fat.
Volume isn’t what they’re looking for, they could care less about a person’s volume ultimately, that measurement is a means to an end...body fat MASS as a percentage.
It is most famously attributed to the ancient Greek scholar Archimedes; he reportedly proclaimed, "Eureka!" when he stepped into a bath and noticed that the water level rose – he suddenly understood that the volume of water displaced must be equal to the volume of the part of his body he had submerged. This meant that the volume of irregular objects could be calculated with precision, a previously intractable problem.