| By :
Roger Brown
The watch altimeter can tell you how high you are in relative terms and in many ways is similar to the function of the type of altimeter found in airplanes. Here are the 3 ways these altimeters are similar: 1.Both deal in sensing their atmospheric environments and measuring atmospheric pressure. With the airplane variety, there is an aneroid wafer that expands or contracts based on how it senses atmospheric pressure. The watch variety is very similar. It senses electrical currents and correlates that with atmospheric pressure. 2. Both are only relative indicators of altitude. Neither of these altimeters will tell you exactly how high you are above the ground. You have to set those to some fixed point before you began an ascent or a descent in order to get them to be a good relative height indicator. However, that is fine for our purposes. If you are climbing a mountain or walking in the woods, your main interest is being able to correlate that height reading on your wristwatch altimeter with the reading on a map. 3. Both have to be calibrated frequently. This is certainly no indicator that they are a low quality instrument. It is just the nature of any instrument dependent upon outside air pressure. Air pressure changes based on a number of factors that change rapidly. For example, if the humidity is high, then the air will weigh more and the pressure will be greater than if the air is dry. In that case, the air provides a lot less in the pressure and what you see indicated on your altimeter watch will be a lot less. In any case, the watch altimeter is a hugely valuable piece of equipment on a hike. You can predict the weather fairly accurately knowing the barometric pressure. That is, if you know how to make sense out of the readings. You need to understand what rising pressure and following pressure means and also how quickly the pressure drop is. You've got to take some time to be able interpret these results. However, it is a very interesting study in meteorology and a really good knowledgebase to have if you currently on the words and far away from traditional sources of getting that kind of information - like, radio and Internet. In general, the way we commonly use the term barometer euphamistically in our lexicon is a good indicator of how to interpret an actual barometer, or an altimeter that uses barometric information. By that I mean if the barometer readings are changing slowly then the weather system that's driving it will also be moving in slowly. In contrast if it's moving quickly, you can interpret the same thing in terms of impending weather on watches with altimeters. The watch altimeter and the airplane altimeter are really the same thing, only different. They are different only in the inputs they receive and how they interpret barometric pressure.
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