La Crosse Technology WS-2310 Operation Manual page 10

Absolute air pressure provides the display of the true measured air
pressure of the current time and location. This is not programmable
and the absolute air pressure range of the weather station is from
8.85 inHg to 32.45 inHg (standard air pressure at an altitude of
30,000ft is around 8.85 inHg).
Relative air pressure is the one value that is calculated back to sea
level from the local absolute air pressure and can thus be taken as a
reference for weather condition and weather development for the
entire country. It can be programmed to represent your local
surroundings. Since the relative air pressure is also the one value
given by various newspapers, TV and radio broadcasting stations in
their daily weather forecasts for their respective locations, users can
set the relative air pressure of the weather station to this value to
represent readings your their area (see Basic Programming Modes
below).
Weather Data (LCD Section 2)
Indoor temperature and humidity are displayed simultaneously in this
section. Use the DISPLAY key to toggle through the displays for other
weather information:
- Outdoor temperature/humidity
- Outdoor wind chill
- Outdoor dew point
- Rainfall 24h
- Rainfall 1h
- Rainfall total.
Notes to Dewpoint and Windchill:
Air can at a certain temperature only carry a certain amount of water
(water vapor), which also increases and decreases with temperature.
If the air temperature decreases below the dewpoint (saturation
point), the excessive water vapor will condense and fall out in form of
dew, fog or rain. At a temperature of e.g. 59°F and a relative humidity
of 50% the dewpoint will be about 41°F, at 80% humidity about
53.6°F. At a relative humidity of 100% saturation is reached, i.e. the
dewpoint is 59°F. At a dewpoint below freezing the fallout will become
frost or snow.
Windchill has been introduced for battle planning during World War II.
It represents not the real measured but the temperature a person
feels in open area under the influence of wind and cold. Windchill is
laid out in tables for various temperatures and wind speeds. At an
outdoor temperature of e.g. 46.4°F and calm winds a person moving
at a speed of 13 mph will already feel a windchill temperature of 32°F.
Wind Data (LCD Section 3)
The current wind direction will be displayed on the LCD compass on
the wind section. Press the WIND key to toggle between wind
direction as numerical (e.g. 225°) and abbreviated characters (e.g.
SW) as well as numerical wind speed display inside the compass
circle.