Density
The density at all points of a homogeneous object equals its total mass divided by its total volume. The mass is normally measured with a scale or balance; the volume may be measured directly (from the geometry of the object) or by the displacement of a fluid. To determine the density of a liquid or a gas, a hydrometer, a dasymeter or a Coriolis flow meter may be used, respectively. Similarly, hydrostatic weighing uses the displacement of water due to a submerged object to determine the density of the object.
Fluid dynamic gauge
A fluid dynamic gauge (FDG) is a measurement technique used to study the behaviour of soft deposit layers in a liquid environment. It employs fluid mechanics to determine the thickness of the layer, and can also be used to obtain a measure of its strength. It was inspired by the technique of pneumatic gauging, which relies on a flow of air rather than the process liquid. Fluid dynamic gauging can be conducted as an in-line measuring technique, but is more commonly used as a research tool.