The right answer is a barometer. Wind gauges measure the force of wind, anemometers measure its speed, and hydrometers measure the moisture content in the atmosphere.

What do we need it for? Pressure tendency can forecast the upcoming changes in the weather. The device is also useful in surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries.

What is the difference between altimeters and barometers? They are similar instruments used for different purposes. An altimeter is transported from one place to another matching the atmospheric pressure to the corresponding altitude. A barometer is always kept stationary and measures subtle pressure changes caused by weather.

Who invented the barometer? Evangelista Torricelli was a talented student of Galileo Galilei. He is credited as the inventor of the device. The first barometer is believed to have been constructed by him in the beginning of the 17th century. So, the barometer is an old device.

More Info: en.wikipedia.org