What is a barometer
A barometer is an instrument that measures air or barometric pressure. The story of the barometer began in 1643, when Torricelli discovered that the pressure of the atmosphere would support a column of mercury approximately 29″ (737mm) high.
Today, the aneroid (or fluidless) barometer is the most common type of barometer; instead of having a pool of mercury that the atmosphere pushes down on, it has a small capsule that acts like a set of bellows inside it. Air has been removed from the capsule and when the air pressure increases, the sides of the capsule are pushed in and the connected needle rises (clockwise). If the air pressure decreases or falls, the sides of the small capsule puff out and the needle moves in an anti-clockwise direction. Air pressure is measured in either inches of mercury or millibars and our barometer dials show both.
Setting your Barometer
The atmospheric pressure varies with altitude (the higher you are, such as up a mountain, the thinner the air becomes and the less air pressure there is) and area, so your barometer must be regulated accordingly. You must first obtain the correct atmospheric pressure for your area. Visit the BBC weather website and type in your town or postcode. Alternatively, telephone your local airfield or coastal station and they will give you this information. Using a small screwdriver, turn the small brass adjusting screw on the back of the instrument until the long end of the black pointer is reading the correct atmospheric pressure for your area. No further adjustment should be required unless the barometer is moved to another area. Care should be taken not to move the black pointer beyond the lower and upper limits of the barometer as this can damage the movement.
All our barometers come with instructions, but if you are having difficulty setting your barometer, our skilled staff are available to help.
How to read your Barometer
The gold pointer in the glass should be turned so that it rests directly above the black pointer. The gold pointer acts as a marker enabling you to remember today’s pressure when you next look at your barometer. You can thus see whether the pressure is rising or falling. It should be understood that the barometer forecasts conditions 12 to 24 hours ahead, it does not indicate present weather conditions.
With air pressure at 1020 millibars or higher, you can expect calm, dry weather. The higher the pressure, the more settled the weather. Fair weather in summer and clear, cold weather in winter, but with the possibility of fog.
When the pressure is between 1005 and 1020 millibars, the weather is changeable, short, bright spells and showers.
When the pressure is below 1000 millibars, the sky is mostly cloudy with a tendency towards rain.
If the pressure falls considerably below 1000 millibars, you can expect storms and strong winds.
A slow, constant increase in pressure indicates a period of settled, dry, sunny weather, whereas a steady decrease indicates persistent bad weather.
A rapid increase in pressure indicates a short period of good weather and a fast decrease indicates storms and strong winds. In summer a rapid decrease can mean the approach of thunderstorms.
A barograph is an aneroid barometer which records the variations in atmospheric pressure onto a chart. It uses one or more aneroid cells or bellows acting through a gear to drive a recording arm onto which is attached a felt pen. The recording chart is mounted on a cylindrical drum which is rotated slowly by a quartz mechanism. Most commonly, the drum revolves one revolution per week.
All our clocks are supplied with batteries and will work as soon as a battery is inserted. We recommend you use quality batteries and that they are changed once a year to avoid leakage. We cannot accept responsibility for movements damaged as a result of batteries that have leaked.