High Pressure - A good time to set your barometer!
They can be traditional or modern... mercury or aneroid...brass cased or stainless steel with hygrometer.
They can be used inside or outside... in the home, garden or workplace.
What they all have in common... is that they are barometers!
A barometer is a scientific instrument used in meteorology to measure atmospheric pressure. Pressure tendency can be used to forecast short term changes in the weather. The measurement is expressed in millibars or inches.
Mercury barometers have a column of mercury inside, and need to be around 32 inches tall. These instruments must be handled very carefully as obviously mercury is poisonous if the instrument gets broken. The mercury barometer uses the height of liquid mercury within the glass tube as an indicator.
If your instrument is shorter than 32 inches tall it is probably an aneroid barometer.
Aneroid barometers have no liquid inside and the reading is displayed by means of dial and a needle - a heavy spring inside expands and compresses with the changes in the air pressure.
Pressure is high and constant over the UK at present so Thursday evening, 1024 millibars, so this is a very good time to set your barometer.
But how do I set it you ask? Is it as easy as a quick twiddle of the knob on the back?
Follow these tips to set your barometer:
To get a value for your barometer, choose a high-pressure day, one when pressure values are not changing very much
Visit the Met Office website, the Met Office's Observation Page, and choose the location of a weather station nearest to you. On a quiet weather day the distance away from you will not be significant.
Using a small screwdriver, turn the screw on the back of the movement and adjust the barometer to the pressure value stated for the weather station
You can check your barometer on other days, but will have to compensate for fast-changing pressures or distance if the pressure is low or changing fast
What does it mean? How do I interpret changes?
Decreasing Pressure - needle moves anti-clockwise. This suggests deteriorating weather, associated with a low or “cyclonic” pressure system.
Increasing Pressure - needle moves clockwise. This indicates improving weather, and is associated with a high or "anti-cyclonic" pressure system.
Steady Pressure - indicates more of the same in the forecast and is typical of extended fine weather periods.
Observe the trend - turn the movable pointer so that it sits directly above the barometer needle. So that you can clearly identify a change in the weather, leave it a few hours before returning to the instrument. Then try tapping the barometer glass gently and note the direction of movement of the needle