Once decided where to position your aneroid barometer, the screw at the back of the barometer (sometimes visible through a small hole) should be turned left or right to adjust the black indicating hand to read the correct sea level reading so, the idea being, everybody with an aneroid barometer reads this at the sea level reading regardless of the altitude at which they are living. (For barographs adjustment of the knurled screw near the top of mechanism will move the pen arm up and down to the required reading.) Weather forecasters often give the air pressure during forecasts particularly during settled weather which is the best time to set barometers. Alternatively, you may get the correct reading from the Met Office or weather station or known good barometer. Some barometers read in inches of mercury, others in millibars, some in mms. Once set, your barometers should not need resetting (unless you move) but you may wish to check it every year or two.

Taking the reading

To use the barometer a reading should be taken every day and this should become habit forming. It is of little use to look at the barometer on Friday to see what the weather will be on Saturday and Sunday. You must build up in your mind the patterns of pressure changes, whether the pressure is in a rising state or falling state etc. Once a day set the brass hand, by moving the centre knob, over the top of the black/blue hand. Then, when looking at it the next day, i.e. 24 hours later, one can see how much the indicating hand has moved up or down and then reset the brass hand again, thus building up the knowledge of the pressure changes over 24 hour periods. Most people read it in the morning and, whilst you can regard it throughout the day, the setting should be limited to once a day.

Tapping the Barometer

Each time you take a reading and set the brass hand, a gentle tap of the barometer on the woodwork or on the edge of the glass frame will take up any mechanical slack in the instrument and thus ensuring every time, that you are taking a more accurate reading. The emphasis is on a gentle tap, a hard tap will not improve the weather! The barometer should move quite satisfactorily on its own, the tapping is merely to take up the final bit of slack which is almost always present.

Understanding the Barometer

As earlier described, a barometer measures air pressure. Traditionally these pieces of furniture have had the words 'Rain', 'Change', 'Fair', etc. inscribed on them. These are very rough averages of weather and as such could almost be disregarded.

It is of less importance what the barometer is reading but more important which direction it is going and by how much and for how long. Thus in the summer one would be ideally looking for a gradual rise in the air pressure over a week to a fortnight followed by a steady hand, not moving. This could be up to 30 or 31 inches. This would almost always indicate settled weather coming that will last for quite a while. Conversely, if you see, as occasionally we do, the barometer falling suddenly over a period of a few hours by an appreciable amount, we are almost always to find a violent storm, usually wind with rain, approaching, but it often will not last long. These quite often cause the most severe damage and thus, in the autumn and winter periods, a constant check on the barometer can be useful. In summary, as Admiral Fitzroy is famous for remarking, "long foretold, long last - short notice, soon past". Weather patterns are normally linked to air pressure as well as wind direction, temperature and time of year. With appropriate study of the subject one can become quite accurate at forecasts but, even for the less scientific amongst us, the varying air pressures are curious and interesting in their own right. Even today the highs and low pressures which we live in may affect many things in our natural world.

Below are some comments attributed to Admiral Fitzroy on the rising and falling barometer.
The Barometer Rises for northerly wind (including from north-west by the north, to the eastward), for dry, or less wet weather, for less wind, or for more than one of these changes:- Except on a few occasions when rain (or snow) come from the northward with strong wind. For change of wind towards any of the above directions:- A Thermometer falls	The Barometer falls for southerly wind (including from south-east, by the south, to the westward), for wet weather, for stronger wind, or for more than one of these changes:- Except on a few occasions when moderate wind with rain (or snow) comes from the northward. For changes of wind direction towards the upper of the above direction:- A Thermometer rises