So when you read a barometer the needle will gradually rise up the scale from day to day. In most cases, a high pressure cell means calm, clear, sunny weather, and as the needle moves up the scale, the increase in pressure is suggesting fine, or “fair” weather is on the way. Similarly, as the high passes over the daily change in the needle’s position will show a decrease in the air pressure, and suggests that if this continues you will experience a period of low pressure. Of course, as in most things to do with weather and life, it’s not quite that simple to read a barometer, which means that although the pressure changes recorded by your barometer have some predictive value, they won’t always be right. For example, if the center of a high passes at a certain distance from where you’re located, you may not experience the fair weather that your barometer predicted before the pressure, and the needle begins to fall. Another general rule of thumb in “how to read a barometer” is that very high pressure readings may indicate windy conditions to follow. The reasoning behind this is that an extreme reading usually means a high pressure gradient to the next low, and high pressure gradients mean strong winds. This rule doesn’t apply in quite the same way to very low pressures. While the pressure gradient will certainly be high, the low is actually the focus of the winds, and unless you happen to be under the eye of a hurricane, the strong winds have already arrived. But you can, if you know how to read a barometer ,turn it into a very useful forecasting tool, but you will need to keep records of the weather to do so. Apart from pressure changes, you can record wind direction, wind direction changes, cloud cover and type of clouds, and the occurrences of rain, snow or thunderstorms.

So let’s recap on what you need to know about how to read a barometer:

Get a regular mercury barometer and start measuring the atmospheric pressure around you by simply measuring how high the mercury column goes up or down. The way you’re going to measure it is from bottom to top using a simpler ruler, keeping in mind that under regular atmospheric pressure the vacuum at the top of the barometer is at almost 30 inches (29.92 to be more precise). When the mercury column drops below that point, we’re experiencing a drop in atmospheric pressure and that means we’re going to get bad weather. This thing works viceversa as well so if the mercury column rises you can expect nicer weather. All in all learning how to read a barometer is a good thing if you’re an outdoor enthusiast and want to know how to plan your trips.

Pocket barometers are based on different principles than the mercury barometers and they’re also known as aneroid barometers because they function without any type of liquid. The aneroid barometers were invented by the French physicist Lucien Vidie in 1843 and are a newer type of barometers. An aneroid barometer is a container that holds a sealed chamber from which some air has been removed, creating a partial vacuum. An elastic disk covering the chamber is connected to a needle or pointer on the surface of the container by a chain, lever, and springs. As atmospheric pressure increases or decreases, the elastic disk contracts or expands, causing the pointer to move accordingly.

Aneroid barometers are even more popular than mercury barometers since they’re based on a newer and safer technology that doesn’t imply mercury which can be if not handled properly hazardous for your health. One of the most popular aneroid barometers is the one shaped like a clock where the barometer pointer moves from left to right in a semicircular motion over a dial, indicating low or high pressure. All of the clock-like aneroid barometers you see hanging on the walls of homes function on these principles. Another type of aneroid barometer has the pointer resting on the side of a rotating cylinder wrapped with graph paper. As the cylinder rotates on its own axis, the pointer makes a tracing on the paper that reflects increases and decreases in pressure. A recording barometer of this design is known as abarograph.

A variation of the pocket barometer is the pocket barometer altimeter also known as a pocket altimeter. The altimeter is a variation of the aneroid barometer and it’s used to measure altitude. This type of altimeters can be found in most modern airplanes and not only.