Kestrel 4500 - Manual (Page 14)

Kestrel ® 4500 Pocket Weather ® Tracker 27
GLOSSARY
The below definitions have been greatly simplified in order to keep this section brief. We strongly
recommend that anyone who wishes to make use of these measurements refer to one of the many
excellent weather references available for a more in-depth definition. On the internet, visit www.
usatoday.com or www.noaa.gov. Or, locate the USA Today publication, The Weather Book. Please note
that any words in a definition printed in italics are themselves defined in this glossary.
Altimeter Setting
An aviation term for the local barometric pressure. Same as reference pressure.
Altitude
The distance above sea level. The Kestrel Meter calculates altitude based on the measured station
pressure and the input barometric pressure - or “reference pressure”.
Barometric Pressure
The air pressure of your location reduced to sea level. Pressure will change as weather systems move into
your location. Falling pressure indicates the arrival of a low pressure system and expected precipitation
or storm conditions. Steady or rising pressure indicates clear weather. A correct altitude must be input
for the Kestrel Meter to display barometric pressure correctly.
Declination
Also called variation, is the angle between magnetic north and true north. Declination is considered
positive east of true north and negative when west. Declination changes over time and with location.
Density Altitude
The altitude at which you would be, given the current air density. Often used by pilots in order to
determine how an aircraft will perform. Also of interest to individuals who tune high performance
internal combustion engines, such as racecar engines.
Dewpoint
The temperature to which air must be cooled in order for condensation to occur. The difference between
dewpoint and temperature is referred to as the “temperature/dew point spread”. A low dewpoint spread
indicates high relative humidity, while a large dewpoint spread indicates dry conditions.
Heat Index
A practical measure of how hot the current combination of relative humidity and temperature feels to a
human body. Higher relative humidity makes it seem hotter because the body’s ability to cool itself by
evaporating perspiration is reduced.
Magnetic North
The point on the Earth’s surface where the Earth’s magnetic field points directly downwards. This pole is
constantly wandering.
Reference Pressure
The local barometric pressure. Input to the altitude screen to provide correct altitude readings. Also
known as the altimeter setting.
Relative Humidity
The amount of water vapor actually in the air divided by the maximum amount of water vapor the air
could hold at that temperature, expressed as a percentage.
Station Pressure
The air pressure of your location, NOT reduced to the sea level equivalent.
Temperature
The ambient air temperature.