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I do know that if your elevation rises while staying in the same position, the pressure is decreasing and that it is a sign of bad weather incoming and a decrease in elevation means that the pressure is increasing.

However, how often should an altimeter be calibrated to the known altitude from a topographical map and do those calibrations need to be recorded?

Also, how much change in elevation is significant?

  • This question is related, but about how the weather affects the altitude readings. What I would like to know is how use the altitude readings to predict the weather. outdoors.stackexchange.com/questions/13195/… – Charlie Brumbaugh Nov 22 '16 at 19:30
  • Significance is dependent on the application. Altimeters are are generally not adjusted, but instead the expectations of travelers are (e.g. Pilots set altimeter readings for their intended landing strip using ATIS reporting before touching down, as a change of a few feet up or down can modify performance) – J.P.M. Nov 22 '16 at 21:29
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On a backpacking trip, calibrate the altimeter only at the trailhead and at places, such as a pass or a lake, that are marked on a topo map. In your comment you mention maybe calibrating the altimeter three times a day, and also by as little as 40 feet. This seems like overkill to me.

On a backpacking trip, we write down the altimeter reading when we stop for the day, and when we start for the day and maybe at the start and stop of a long break or flattish region if the weather looks like it is changing. If these notes are organized, it is easy to integrate mentally the changes caused by weather change rather than actual altitude change. (Yes, they are cumulative.) We calibrate the altimeter only when a significant change has accumulated -- 100 feet or so -- and when we are at a lake or pass or other benchmark.

We don't feel we need to know the altitude with great accuracy on a step by step basis. As for what change is significant for forecasting the weather purposes, it depends on the precision and accuracy of your altimeter. For a long time we had an analog altimeter which could be read to 10 feet precision, but which was not accurate to 10 feet. A rise or drop of 100 feet overnight was definitely significant, weatherwise. 50 feet, probably significant. (This is for the Sierra.)

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