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ABOUT ALTITUDE AND AIR PRESSURE
MEASUREMENTS
Altimeter
Generally, air pressure and temperature decrease as altitude increases. This
watch bases its altitude measurements on International Standard Atmos-
phere (ISA) values stipulated by the International Civil Aviation Organization
(ICAO), which define relationships between altitude, air pressure, and tem-
perature.
ALTITUDE
AIR PRESSURE
472 hPa/mb
6000 m
About 6.7 hPa/mb per 100 m
5500 m
540 hPa/mb
5000 m
About 7 hPa/mb per 100 m
4500 m
616 hPa/mb
4000 m
About 8 hPa/mb per 100 m
3500 m
701 hPa/mb
3000 m
About 9 hPa/mb per 100 m
2500 m
795 hPa/mb
2000 m
About 10 hPa/mb per 100 m
1500 m
About 11 hPa/mb per 100 m
899 hPa/mb
1000 m
500 m
About 12 hPa/mb per 100 m
0 m
1013 hPa/mb
Source: International Civil Aviation Organization
ALTITUDE
AIR PRESSURE
13.76 inHg
20000 ft
About 0.119 inHg per 200 ft
18000 ft
16.22 inHg
About 0.1315 inHg per 200 ft
16000 ft
14000 ft
19.03 inHg
12000 ft
About 0.15 inHg per 200 ft
10000 ft
22.23 inHg
8000 ft
About 0.17 inHg per 200 ft
6000 ft
About 0.192 inHg per 200 ft
25.84 inHg
4000 ft
2000 ft
About 0.21 inHg per 200 ft
0 ft
29.92 inHg
Source: International Civil Aviation Organization
There are two standard methods of expressing altitude: Absolute altitude
and relative altitude. Absolute altitude expresses an absolute height above
sea level. Relative altitude expresses the difference between the height of
two different places.
Height of building 130 m
(Relative altitude)
Barometer
Barometric pressure indicates changes in the atmosphere, and by monitoring
these changes you can predict the weather with reasonable accuracy. Rising
barometric pressure indicates good weather, while falling pressure indicates
deteriorating weather conditions.
The barometric pressures that you see in the newspaper and on the TV
weather report are measurements corrected to values measured at 0 m sea
level.
TEMPERATURE
–24 C
–17.5 C
–11 C
About 6.5 C
–4.5 C
per 1000 m
2 C
8.5 C
15 C
TEMPERATURE
–12.2 F
2.0 F
16.2 F
About 3.6 F
per 1000 ft
30.5 F
44.7 F
59.0 F
Rooftop at an altitude of
230 m above sea level
(Altitude above sea level)
Sea
1675-7
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