For your information, a barometer is a device that measures the air pressure within a particular area of the environment. It is also a tool in which to forecast future weather conditions, as well as describe the current weather condition within the area in which you happen to be.
Yes, and believe it or not, a barometer is also used to measure the altitude above sea level, since it is true that the higher you are above sea level the lower the air pressure within the atmosphere until at last you reach an altitude where air does not exist within the vacuum of space.
For such measurements of air pressure the most accurate barometer is a mercury barometer. The other type of barometer is called an aneroid barometer. So you know, aneroid barometers are case enclosed compact gauges with a glass protected pointer and printed scale of measurement in the form of a readable face known as a dial.
The low end of the scale can report an air pressure reading as low as zero and from that point graduate upward to as high as 32. Naturally, in a vacuum the pointer of the barometer would point to zero. Keep in mind that the normal air pressure recorded at sea level ranges between 29 and 30.5. Within this range one would likely experience calm and clear atmospheric conditions. In other words, you would or expect to experience a relatively nice day.
A reading below 29 signals a coming change of weather or a weather condition that is less than desirable, in terms of the severity of the wind, temperature and precipitation. You see, cold air is denser than hot air, causing a higher air pressure and visa versa.
On the other hand, a low pressure condition exists when hot air rises causing cold air to be sucked into the void created at ground level. This also provides the opportunity for a rain, snow and/or other weather event. Generally speaking, the lower the reading the more severe the weather event. Hurricanes are the cause of the lowest barometric readings ever recorded and they are the most violent of storms that Humanity can experience.
As such, a quick glance at your barometer will most likely tell you the current weather condition or if a change of that weather is likely to occur. More often than not, at least one of my aneroid barometers is entirely correct. Also, it is the best way for a novice such as me to forecast the weather within any particular region on our Earth. Then again, you can seek the prediction of a professional to either confirm or refute your own results.