Kestrel 4000 NV Instruction Manual page 12

Kestrel 4000 Pocket Weather Tracker
® ®
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.
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.
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.
Wet Bulb Temperature
The lowest temperature to which a thermometer can be cooled by evaporating water into the air at constant
pressure. This measurement is a holdover from the use of an instrument called a sling psychrometer. To
measure wet bulb temperature with a sling psychrometer, a thermometer with a wet cloth covering over
the bulb is spun rapidly through the air. If the relative humidity is high, there will be little evaporative
cooling and the wet bulb temperature will be quite close to the ambient temperature. Some exercise
physiology guides use wet bulb temperature, rather than heat index, as a measure of the safety of exercise in
hot and humid conditions.
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