Density
A number of techniques as well as standards exist for the measurement of density of materials. Such techniques include the use of a hydrometer (a buoyancy method for liquids), Hydrostatic balance (a buoyancy method for liquids and solids), immersed body method (a buoyancy method for liquids), pycnometer (liquids and solids), air comparison pycnometer (solids), oscillating densitometer (liquids), as well as pour and tap (solids). However, each individual method or technique measures different types of density (e.g. bulk density, skeletal density, etc.), and therefore it is necessary to have an understanding of the type of density being measured as well as the type of material in question.
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.