A weathervane, or weathercock, is an instrument used to measure the direction of wind as it changes. The device often sits atop a building, and for centuries has been used for both practical and decorative purposes. Whilst "weathervane" is the most common term, there are other synonyms for this instrument, including wind vane, weathercock, and weather gauge. Wind vane is typically used when referring to the scientific instrument used to measure wind direction, whilst weathercock shares a similar history with weathervanes and is considered a more traditional term. Weather gauge is a more general term, often used to refer to any instrument which measures weather conditions.