why is air pressure meausured with a barometer?

Answer 1

We live at the bottom of an ocean of air. We use the fluctuations of this pressure on the bottom of this ocean of air to forecast weather.

You can make a crude device to measure this pressure by using a sealed container and measuring the distortion at different time intervals. A correction for temperature must be considered.

Aneroid and Mercury barometers are virtually not affected by temperature.

Answer 2

Precisely because a barometer is a pressure measuring device !!?