Ambient Weather DHR70B-BRASS 사용자 설명서 - 페이지 3

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The barometer includes a manually set needle, which is used to mark the current measurement so a

change can be seen. Barometric readings should be taken daily. Remember that the rate of change of

barometric pressure is important in determining weather changes. You may want to take multiple

readings each day during periods of unstable weather conditions.

The following basic rule of thumb will hold true in using the barometer to predict weather conditions.

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A fast rise in barometric pressure means goo weather of short duration.

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A rapid drop in barometric pressure means disturbances nearby, showers of short duration.

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Regular elevation in barometric pressure usually will indicate a clear, dry weather conditions

(cold and dry in the winter).

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A slow but continuous drop in barometric pressure will indicate persistent, bad weather.

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Slow drops of 2-3 tenths mbar per 24 hours a depression of some distance away.

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Drops of 1-2 tenths mbar per hour means disturbances nearby of short duration.

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Steep drops of 6-10 tenths mbar within 4-5 hours period indicates coming rain and/or storm

with strong winds.

4.3 Absolute vs. Relative Pressure

To compare pressure conditions from one location to another, meteorologists correct pressure to

sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected

pressure (the pressure your location would be at if located at sea-level) is generally higher than your

measured pressure.

Thus, your absolute pressure (measured at your location) may read 28.62 inHg (969 mb) at an altitude

of 1000 feet (305 m), but the relative pressure (sea-level) is 30.00 inHg (1016 mb).

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.

4.4 Barometer Calibration

Reference Figure 1 to calibrate the barometer (your barometer calibration screw location may vary).

Your barometer will operate from -100 to 3,000 feet with reliable accuracy. Aneroid barometers have a

small screw on the back for sea-level calibration. With a flat blade screwdriver, turn this screw in

either direction slightly while looking at the indicator needle. It should move in one direction or the

other. Tap the barometer to see where the needle settles. Continue this procedure until the proper

pressure reading is obtained. Do not turn the screw counter-clockwise (to the left) too far, since the

screw can fall out. After the initial calibration, no further adjustment will be required unless the

barometer is moved to a new geographic location.

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