To gauge the density of milk, a lacto densitometer is employed. It is used to figure out how much fat is in milk. The said device determines the refractive index of milk. A medium's refractive index serves as a gauge for how easily light may bend through it. The refractive index of milk increases with milk density. Several instruments that measure the amount of fat in milk are calibrated using the lacto densitometer. It is also employed to figure out other liquids' densities.