Editing Flight instruments (section)

==Pitot-static systems==
Instruments which are [[pitot-static system]]s use air pressure differences to determine speed and altitude.

===Altimeter===
{{main|Altimeter}}
;[[Image:3-Pointer Altimeter.svg|left|100px]]
The altimeter shows the aircraft's altitude above sea-level by measuring the difference between the pressure in a stack of [[Pressure measurement#Aneroid|aneroid]] capsules inside the altimeter and the atmospheric pressure obtained through the [[Static pressure|static]] system. The most common unit for altimeter calibration worldwide is [[Pascal (unit)|hectopascals]] (hPa), except for North America and Japan where [[inches of mercury]] (inHg) are used.<ref>[https://aerosavvy.com/metric-imperial/ Aviation's Crazy, Mixed Up Units of Measure - AeroSavvy]</ref> The altimeter is adjustable for local barometric pressure which must be set correctly to obtain accurate altitude readings, usually in either feet or meters. As the aircraft ascends, the capsules expand and the static pressure drops, causing the altimeter to indicate a higher altitude. The opposite effect occurs when descending. With the advancement in aviation and increased altitude ceiling, the altimeter dial had to be altered for use both at higher and lower altitudes. Hence when the needles were indicating lower altitudes i.e. the first 360-degree operation of the pointers was delineated by the appearance of a small window with oblique lines warning the pilot that he or she is nearer to the ground. This modification was introduced in the early sixties after the recurrence of air accidents caused by the confusion in the pilot's mind. At higher altitudes, the window will disappear.<ref name=faa/>{{rp|3-3}}

===Airspeed indicator===
{{main|Airspeed indicator}}
;[[Image:Airspeed indicator.svg|left|100px]]
The airspeed indicator shows the aircraft's speed relative to the surrounding air. [[knot (unit)|Knots]] is the currently most used unit, but kilometers per hour is sometimes used instead. The airspeed indicator works by measuring the ram-air pressure in the aircraft's [[pitot tube]] relative to the ambient static pressure. The [[indicated airspeed]] (IAS) must be corrected for nonstandard pressure and temperature in order to obtain the [[true airspeed]] (TAS). The instrument is color coded to indicate important airspeeds such as the stall speed, never-exceed airspeed, or safe [[Flap (aeronautics)|flap]] operation speeds.<ref name=faa/>{{rp|3-7 to 3-8}}

===Vertical speed indicator===
{{main|Vertical speed indicator}}
;[[Image:Vertical speed indicator.PNG|left|100px]]
The VSI (also sometimes called a [[variometer]], or rate of climb indicator) senses changing air pressure, and displays that information to the pilot as a rate of climb or descent in feet per minute, meters per second or knots.<ref name=faa/>{{rp|3-8 to 3-9}}
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