Cross-correlation flow measurement is a powerful technique for measuring flow based on the natural fluctuations. They are designed to use the properties of suspended solids to measure the flow. It is based on measuring the transition time of some types of disturbances, such as electrical resistance between two points in a flow system. Ultrasonics is commonly used with cross correlation flow meter. Random variations of conductivity, pressure and temperature are the basis of this type of flowmeter. Cross-correlation techniques are used for the linear measurement of speed with two retro-reflected infrared beams. This flowmeter is applied for the measurement of the velocity of hot steel strip in a high-speed rolling mill. They are available for the measurement of the mass flow of solids in pneumatic conveying systems.