Modern instruments used to measure wind speed and direction are called anemometers and wind vanes, respectively. These types of instruments are used by the wind energy industry, both for wind resource assessment and turbine control. When a high measurement frequency is needed (such as in research applications), wind can be measured by the propagation speed of ultrasound signals or by the effect of ventilation on the resistance of a heated wire.[5] Another type of anemometer uses pitot tubes that take advantage of the pressure differential between an inner tube and an outer tube that is exposed to the wind to determine the dynamic pressure, which is then used to compute the wind speed.[6]