# Barametric Altitude

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Hi, according to the instruction book,a symbol appears'whenever the aircraft

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What book? For what instrument?

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The book is the instruction manual for a simple altimeter and has a V shaped marker that rotates around the altimeter dial, and appears:'whenever the aircraft

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>The book is the instruction manual for a simple altimeter and>has a V shaped marker that rotates around the altimeter dial,>and appears:>>'whenever the aircraft

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Hi Stick, basically I'm after some help with the definition and maybe some coding if I'm lucky.The statement'whenever the aircraft

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Nick,On a given day the air pressure varies at a given place. This is due to temperature and air density (due to moisture) variations that occur naturally.As you may know, you can use the difference in barometric pressure to determine altitude, as the amount of air above you changes relative to your altitude.So, to measure the height of a building, you could measure the indicated pressure at the base and top, subtract, and use a simple formula to determine the height. (see: http://en.wikipedia.org/wiki/Altimeter)In an aircraft flying, you can't get out and measure the altitude at ground level to compare, and that would give you AGL (above ground level) altitude anyway. So, one pilot would not be able to avoid another as their altitudes wouldn't be relative to each other.To deal with all this, there is the concept of the "Standard Day" which basically is the benchmark temperature, moisure (humidity), and pressure. That is 29.92 inches of mercury.Below 18,000 feet, we set our altimeters to the current reported pressure at the closest ground station, and above at the standard 29.92. In this way, our altimeter "knows" what the pressure is on the ground (or what flight level we are at if > 18,000 ft), and reads the same for pilots.So, basically, you 'set' the altimeter to calibrate it to either the local pressure so that it accurately tells you the altitude given current conditions, or to the standard 29.92 when at flight level altitudes so that you are on the same wavelenght as other pilots, and not at their altitude. This makes it easier as you don't have to keep updating it when you are flying over ground stations at 600 knots.

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Hi Stick,'barometric altitude setting', would this be the local pressure set on the altimeter device, and this value would have an equivalent altitude. If so, how would the altitude be found?cheers,nick

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If it's a C/C++ gauge the variable is ALT_FROM_BAROMETRIC_PRESSURE, if it's an XML gauge the variable is INDICATED ALTITUDE.What your documentation says is that this indicator shows up when it's set value is within 450ft of the variables stated above. You have a variable defined for the altitude desired... and this pointer represents that value. It is only visible whenever the plane's actual measured altitude (based on KOHLSMAN setting) is within 450 of the variable's value. The pointer's variable, as I stated, is something you declare... it is not inherently defined within FS.

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Many thanks,cheers,nick

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