Hello.

Barometer is an instrument used to measure air pressure of a particular region. If the needle of barometer rises or increases it shows increase in air pressure. If needle of barometer falls or decreases then it shows decrease in air pressure.

Reading of barometer at different places is different due to climatic conditions and it also depends on factors like altitude, depth etc.

A barometer reading of 30 inches (Hg) is considered normal.

hope this was helpful.