Vane Anemometers Forms of rotating mechanical velocity anemometers may be described as belonging to the vane or propeller class. With this style of anemometer, the axis of rotation must be parallel to the direction of the wind and therefore typically horizontal. In open spaces the wind varies in direction and the axis has to follow its changes. In cases where the direction of the air motion is always the same, as in the ventilating shafts of mines and buildings for instance, wind vanes, known as air meters are employed, and give most satisfactory results. Vane anemometers are available with additional functions such as temperature, humidity and dew point measurements, volumetric conversion and data logging ability. Thermal Anemometers Thermal anemometers use a very fine wire (on the order of several micrometers) or element heated up to some temperature above the ambient.