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Aneroid Barometer:

The aneroid barometer measures atmospheric pressure by means of changes in shape of an elastic metal disk that covers a partially evacuated chamber and incorporates a miniature drive chain linkage between the mechanism that can affect the free movement of the pressure indicator hand. It is highly advisable to lightly tap the glass near the center brass knob with your fingers before taking a barometer reading. This light tap will overcome any friction that may affect accurate hand readings, especially during periods of slow atmospheric changes. Coast Guard personnel have advised us that tapping the barometer is necessary even on their most expensive barometers.

The ability of the barometer to indicate changes in atmospheric pressure makes it a useful instrument in weather forecasting. The following basic rule of thumb will hold true in using the barometer to predict weather conditions:

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

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

c. Regular elevation for barometric pressure usually will indicate clear, dry weather conditions (Cold and Dry in the Winter)

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

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

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

g. Steep drops of 6-10 tenths within 4-5 hours period indicates coming rain and/or storm with strong winds. (When we had 90 mile an hour winds blowing through town a couple years ago, I went thru the shop and tapped each of our barometers. They all fell over 10 tenths.)

Barometric readings should be taken daily. Remember that the rate of change is as important as amount of change in determining weather changes. You may want to take multiple barometric readings each day during periods of unstable weather condition.

1. The reading on my dial does not match the weather.

One of the most common comments is that "my barometer hand is pointing to fair but it's raining outside". The words on a barometer dial are only to show that the lower the number the poorer the weather. They are put on the dial for reference and to balance the dial. The numbers however are significant and are the things you should pay attention to. Generally, 30 and up is fair weather and below 30 is poorer weather. Contact your local weather bureau/climatologist or check with your local TV/Radio for the exact local barometric pressure.

2. How do I adjust my aneroid barometer ?

Aneroid barometers have a small screw on the back. 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 until proper pressure reading is obtained. Do not turn the screw counter-clockwise (to the left) too far since it could come out. Your barometer will operate from sea level up to 7000 feet with reliable accuracy. After the initial calibration no further adjustment will be required unless the barometer is moved to a new geographic location.

3. Where should I hang my barometer ?

Anywhere that it looks good to you. Locate the barometer in a location where it will remain basically undisturbed. There are old stories "never hang the barometer on an outside wall". Well the air pressure is the same on any wall, inside or outside.

4. What’s the brass pointer for?

The brass pointer indicates the change in pressure relative to the last time you checked it. Place the brass pointer attached to the glass in a position directly over the pressure indicator hand. The brass pointer is intended as a reference that will allow you to determine direction/distance the pressure indicator has moved since your last reading.

5. How do I know if my aneroid barometer works ?

If you are not sure if your aneroid barometer is working it can be checked very easily. Place the instrument in a tightly sealed clear plastic bag (ziploc). Get as much air in the bag as you can before you seal it up. While observing the dial of the barometer, squeeze the bag and watch for the needle to move (increase). If the needle does not move there is a problem with the linkage in the instrument or with the bellows.

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