what is the first one?
A scientific instrument that is used to measure air pressure in a certain environment.
Barometer
A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries.

what is the name for a weather forecaster Those using mathematical models and knowledge to prepare daily weather forecast are called "weather forecasters" or "operational meteorologists". what is weather forecasting? The application of science and technology to predict the conditions of the atmosphere for a given location and time. what are a few modern methodologies used in this regard? Barometer, Beaufort scale, Accuweather, El Niño-Southern Oscillation
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Barometer [SEP] Introduction
A barometer is a scientific instrument that is used to measure air pressure in a certain environment. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, pressure systems and frontal boundaries. Barometers and pressure altimeters (the most basic and common type of altimeter) are essentially the same instrument, but used for different purposes. An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitude, while a barometer is kept at the same level and measures subtle pressure changes caused by weather and elements of weather.