Why should barometric pressure be corrected for the vapor pressure of water?

Answer 1

In order to answer your question, first I will briefly explain how an altimeter works.

An altimeter senses current atmospheric pressure, and converts it into an altitude reading. The lower the pressure, the higher altitude it will show.

In aviation, the pilot needs to select the correct altimeter setting before takeoff and during flight in order to get a correct reading. This is required because the pressure at sea level changes based on weather conditions. For example, if I parked my aircraft at an airport, then came back the next morning, my altimeter would give me a different reading than before because the weather conditions changed slightly overnight. I would then have to change the altimeter to the current local altimeter setting. The local altimeter setting is defined as the atmospheric pressure at Mean Sea Level (MSL) in inches of Mercury. Once the altimeter has the pressure at sea level, it can give an accurate reading of the current altitude. Air Traffic Control keeps pilots updated on the local altimeter settings as they fly. The other way to calibrate an altimeter, this only works on the ground, is to turn the pressure selector until the altimeter show the elevation of the airport you are currently at. At this point, the pressure shown is the local altimeter setting.

Answer 2

Well, the pressure of the courant of the water affects the barometer reading in a way that could make it false. The barometric pressure of the water needs to be tested in order for the vapor to condense.

Answer 3

Because if it is corrected it is more precise and accurate because water also exerts a pressure on the atmosphere therefor your results would differ