Usually density meters, also known as densimeters or specific gravity meters, are adjusted with air and water at a specific measuring temperature. This temperature is controlled with a Peltier element, which can cool down or heat up the measuring cell to a specific temperature (e.g., 20°C). First, the frequency of the measuring cell filled with air is measured. This frequency is assigned to the density value of air. Then the measuring cell is filled with water and the frequency of the measuring cell filled with water is measured. This second frequency is assigned to the density value of water. This two-point adjustment can also be done with air and a standard, or with two standards covering different density ranges.
Learn more about how to adjust your digital density meter.