Above sea level, it assumes a constant temperature lapse rate from sea level of 6.5C per 1000 m (1.98C/3.56F per 1000 ft) rise in height, up to an altitude of 11,000 m (-56.5C) . 11,000m is assumed to be the Tropopause, above which constant temperature (-56.5C) is assumed.

Pressure figures from this ISA are used in calibration of barographs, because although the real atmosphere varies from day to day, for calibration purposes a set of internationally agreed figures are needed so that all calibrations are to the same datum, whether or not such figures correspond to `true' height on a given day. A similar principle is used in calibrating pressure altimeters for aircraft, so that all aviation activities have a common standard of pressure height indication in the cockpit.

The ellipsoid radii for WGS 84 are as follows:

Major Axis (the Equator), radius = 6378.1370 km

Minor axis (Polar), radius = 6356.7523 km (flattening 21.3847 km)

Orientation The minor axis is between the Earth's centre of mass and the Terrestrial Pole as defined by the Bureau Internationale de l'Heure (BIH). In approximate terms, this is the Earth's spin axis.

The maximum differences between the WGS84 Geoid and the WGS84 Ellipsoid are +65m at 60N 030W (S of Iceland, geoid above the ellipsoid) and -102m on the equator at 080E (S of India, geoid below the ellipsoid). A table of WGS84 Geoid heights with respect to the WGS84 Ellipsoid is available in MS Excel format from FAI (via the GFAC Chairman).

Long Distances (over 10 Km) | Kilometre (km) |

Short distances (less than 10 Km) | Metre (m) |

Very short distances | Centimetres (cm) |

Altitude | Metre (m) |

Horizontal speed | Kilometre/hour (km/h) |

Vertical Speed | Metre/second (m/s) |

Temperature | Degrees Celsius (°C) |

Pressure | Hectopascal (hpa) or Millibar (mb) |

Mass | Kilogramme (kg) |

Time | Hours, Minutes, Seconds UT (hr, min, sec) |

DISTANCE1 foot = 0.3048 metre mile (nautical) = 1852.0000 metre kilometre = 3280.8 feet mile (statute) = 5280 feet mile (statute) = 1.6093 kilometres mile (nautical) = 1.1508 miles (statute) centimetre = 5 kilometres (on 1:500,000 map) inch = 4 miles (on 1:250,000 map) degree = 111.1949 kilometres (Great Circle arc)SPEED1 foot/second = 0.3048 metres/second metre/sec = 3.6 kilometres/hour metre/sec = 1.9438 knots metre/sec = 2.2369 miles/hour mile/hour = 1.6093 kilometres/hour knot = 1.8520 kilometres/hour knot = 1.1508 miles/hour knot = 101.2686 feet/minute mile/hour = 1.4667 feet/secondPRESSURE1 atü = 15 psi (for tire pressure) psi = 6.8948 kilopascals atmosphere = 101.325 kilopascals inch Hg (0°C) = 33.8639 millibars (mb) atmosphere = 29.9213 inches Hg (0°C) atmosphere = 1013.3252 millibars millibar = 0.7501 millimetres HgVOLUME1 gallon (Imp) = 1.2009 gallons (US) gallon (US) = 3.7854 litres gallon (Imp) = 4.5459 litresMISC.1 gallon (Imp) = 10 lbs water (15°C) as a rough approximation: 100 ft/min = 1 knot = 1/2 metre/sec

From | To Fahrenheit | To Celsius | To Kelvin |
---|---|---|---|

Fahrenheit (F) | F | (F - 32) * 5/9 | (F - 32) * 5/9 + 273.15 |

Celsius (C or ^{o}) |
(C * 9/5) + 32 | C | C + 273.15 |

Kelvin (K) | (K - 273.15) * 9/5 + 32 | K - 273.15 | K |

Pressure to altitude conversion:

h = 288.15/0.0065 * (1-(p/101325)^(0.0065*287.053/9.80665))

h - altitude (m)

p - pressure (Pa)