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The standard sea-level pressure is 29.92 in Hg (1013 mb). This is the average sea-level pressure
around the world. Relative pressure measurements greater than 29.92 inHg (1013 mb) are
considered high pressure and relative pressure measurements less than 29.92 inHg are considered low
pressure.
To determine the relative pressure for your location, locate an official reporting station near you (the
internet is the best source for real time barometer conditions, such as Weather.com or
Wunderground.com), and set your weather station to match the official reporting station.
5.5
The Barograph
The barograph allows you to predict weather by displaying the change in pressure over time.
In general, when pressure is increasing, the weather is improving, and when pressure is decreasing, the
weather is deteriorating. This is referred to by meteorologists as high pressure and low pressure
conditions. Storms and hurricanes will result in a rapid decrease in pressure. Hot, dry weather is
usually a result of high pressure.
The graph displays the pressure trend over the last 72 hours (the oldest data is on the left of the graph
and the newest data is on the right of the graph. The horizontal axis is time, and is plotted -3, -6, -9,
-18, -36, -54, and -72 hours ago.
The vertical axis is the change in pressure from the current pressure. Thus, the current pressure is
displayed as 0. The vertical axis is auto-scaled, and will change automatically based on the magnitude
of the change in pressure over the 24 hour period.
The example in Figure 8 shows a drop in pressure 6 hours ago of about -4 hPa.
Figure 8
5.6
Viewing Minimum and Maximum Records (Memory Mode)
While in normal time mode, perform the following operations to view the minimum and maximum
values since the last time they were reset.
