La Crosse Technology WS- 1910TWC-IT Instruction Manual page 21

AIR PRESSURE HISTORY (ELECTRONIC BAROMETER WITH
BAROMETRIC PRESSURE TREND)
The bottom section of the LCD also shows the relative air pressure value and the air
pressure history.
The bar graph of the electronic barometer shows the air pressure history of the past 12
hours in five 3-hour steps.
Air pressure
changes in inHg
The horizontal axis represents the last 12 hours air pressure recording (-12, -9, -6, -3 and
0 hour). The bars are plotted at each of the 5 steps and give the trend over the recorded
period. The scale on the right compares the result. The "0" in the middle of this scale
determines the current air pressure.
The vertical axis represents the air pressure changes in inHg (+0.12, +0.06, 0, -0.06, -0.12.
The "0" represents the current air pressure). The newly measured pressure was compared
to the previously recorded pressure reading. The pressure change is expressed by the
difference between the current ("0h") and the past readings in division of ±2 hPa or ±0.06
inHg. If the bars are rising it indicates that the weather is getting better due to an increase
in air pressure. If the bars go down it indicates a drop of the air pressure and the weather
is expected to get worse from the present time "0".
At every full hour, the current air pressure is used as a basis for the display of a new graph
bar. The existing graph is then moved one column to the left.
NOTE:
For accurate barometric pressure trend, the Weather Center should operate at the same
altitude. For example, it should not be moved. Should the unit be moved, for instance from
the ground to the second floor of the house, the readings for the next 48-60 hours shall be
discarded.
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Air pressure
changes in hPa