Weather has a direct impact on us when we're working, playing, driving and walking. Meteorologists use instruments specific to each of the basic weather elements---atmospheric pressure, humidity, temperature and wind---to help predict what we might expect as we go about our daily routines. While those predictions aren't always right, these instruments are very accurate when properly calibrated.
A barometer is used to measure atmospheric pressure. This measurement is important because it hints at impending weather patterns. When the atmospheric pressure is dropping, you can expect rain, storms or windy weather. Rising atmospheric pressure indicates that sunny skies and mild weather are likely. Historically, most barometers used mercury-filled tubes to measure the atmospheric pressure. Due to safety concerns and thanks to modern electronics, few barometers are manufactured with mercury today. The most common units of measure on a barometer are "inches of mercury" and "millibars."
Humidity, or air moisture content, is often measured with either a psychrometer or a hygrometer. A psychrometer consists of two thermometers---one with a small moist cloth pulled over the reservoir bulb (wet bulb) and the other without (dry bulb). Hygrometers are commonly electronic. Both devices measure the moisture content of the air as a percentage of full saturation.
Arguably the most well-known weather element measuring device is the thermometer, which is used to measure temperature. Unlike some of the other instruments used to measure the elements of weather, the thermometer is also an indispensable tool for things unrelated to weather, such as baking, refrigeration, heating, cooling, automotive work and health care. A thermometer measures the temperature in degrees and will commonly display the degrees using both the Fahrenheit and Celsius scales. The thermometers used by scientists are often configured to use the Kelvin scale.
Wind speed is measured with an anemometer. The most widely used anemometer for weather-related measurement is composed of four cups (or a propeller) attached to a central shaft that rotates in the wind, which in turn drives an electric generator that has been calibrated to measure the speed of the wind. Wind speed is most often measured in "knots" ( a knot is equal to about 1.15 MPH) and "MPH," or miles per hour.