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.
Gravitic density meter
A Gravitic density meter is a type of density meter used in multiple industries to measure the density of a slurry flowing through a pipe line. It consists of a flexible rubber hose that deflects when weight is flowing through the hose. A displacement measurement device, usually a high precision laser or load cell, is used to measure how much change has occurred in the system. 
By calculating the change of deflection of the hose, a gravitic density meter can be used to 
find the real time, continuous density.