An anemometer in which a windmill is driven by the air stream, and its rotation is transmitted through gearing to dials or other recording mechanism. In some instruments, the rotating vanes and dials are in the same plane; i.e., both vertical, while in others the dial is horizontal. In the windmill type, the operation of air measurement involves readings of dials at the beginning and end of a measured period. Windmill instruments may be fitted with an extension handle, providing a form of remote control; used to measure air speed in an otherwise inaccessible spot.