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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.
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.
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.
540 hPa/mb
616 hPa/mb
701 hPa/mb
795 hPa/mb
899 hPa/mb
1013 hPa/mb
472 hPa/mb
0 m
500 m
1000 m
1500 m
2000 m
2500 m
3000 m
3500 m
4000 m
4500 m
5000 m
5500 m
6000 m
8.5°C
2°C
–4.5°C
–11°C
–17.5°C
–24°C
15°C
About 6.5°C
per 1000 m
About 6.7 hPa/mb per 100 m
About 7 hPa/mb per 100 m
About 8 hPa/mb per 100 m
About 9 hPa/mb per 100 m
About 10 hPa/mb per 100 m
About 11 hPa/mb per 100 m
About 12 hPa/mb per 100 m
ALTITUDE AIR PRESSURE TEMPERATURE
Source: International Civil Aviation Organization
0 ft
2000 ft
4000 ft
6000 ft
8000 ft
10000 ft
12000 ft
14000 ft
16000 ft
18000 ft
20000 ft
25.84 inHg
22.23 inHg
19.03 inHg
16.22 inHg
13.76 inHg
44.7°F
30.5°F
16.2°F
2.0°F
–12.2°F
59.0°F29.92 inHg
About 3.6°F
per 1000 ft
About 0.119 inHg per 200 ft
About 0.1315 inHg per 200 ft
About 0.15 inHg per 200 ft
About 0.17 inHg per 200 ft
About 0.192 inHg per 200 ft
About 0.21 inHg per 200 ft
ALTITUDE AIR PRESSURE TEMPERATURE
Source: International Civil Aviation Organization
Height of building 130 m
(Relative altitude)
Rooftop at an altitude of
230 m above sea level
(Altitude above sea level)
Sea