Linearity measures how linear the output signal is expected to be in proportion to flow rate. The output signal from a flow meter may or may not be linear depending upon the operating principle of the flow meter used. For example, the output signal of the primary element of a differential pressure flow meter is not linear to flow rate. Rather, the square root of the differential pressure produced by the meter is linearly proportional to the flow rate. Therefore, the raw signal produced by a differential pressure flow meter has to be conditioned (“scaled”) by another device to provide a linear signal.