• Old-fashioned weather instruments can still yield accurate results.Hemera Technologies/Photos.com/Getty Images
  
  Measuring weather data has long been an activity that has been important in various stages of civilization. Nowhere is this more evident than with the weathervane, which might possibly be the world's oldest and perhaps simplest weather forecasting tool. Dating back at least as far as the Greeks and Romans, the weathervane accurately indicates wind direction. Every time the weathervane points in a new direction, chances are good that a change in weather is on the way.
  
  

Anemometers

• Technically, anemometers are instruments that measure wind velocity, yet most of these weather tools come with a weathervane-like attachment that indicates wind direction as well. These bits of information are important to both backyard and professional meteorologists, because wind speed gives some indication to the differences in pressure gradients within the area. With an anemometer, wind speed is measured by a series of cupped devices that catch the breeze and consequently spin around an axis. The rotational speed is then calibrated by mechanical devices.
  
  

Barometers

• Another important tool for the weatherman is the barometer. This tool measures air pressure and is of the utmost importance, especially when readings are made on a regular basis over the course of a day. A significant change in barometer readings usually indicate that a change in weather patterns are occurring. Modern weather forecasters compile data accumulated by a large number of barometers located both on the ground and attached to airborne weather balloons. This critical info is fed into a computer, which converts the data to a weather map.
  
  

Thermometers

• Thermometers can be used in two ways. With one thermometer you can record the daily temperatures as they change over a 24-hour period. To obtain a clear idea of temperature changes, this should be done every hour or two around the clock. Of course, with today's digital technology, there are numerous weather tools that can do this automatically. Still, an old-fashioned mercury bulb thermometer is nice to have on hand, just as an occasional visual reference.
  
  Instruments that measure relative humidity use two thermometers. One is called a wet-bulb thermometer and the other is a dry-bulb thermometer. A comparison of these two temperatures produces the actual value of relative humidity. Wet bulb - dry bulb hygrometers are stationary devices that measure this piece of data with some accuracy. Sling psychrometers are more accurate, but entail swinging a pair of wet and dry bulb thermometers through the air for a short period of time.
  
  

Rain Gauge

• A rain gauge is not much help in predicting the weather, but these cylindrical devices are capable of recording how much weather or, more specifically, how much rain has fallen. For anyone trying to keep accurate weather data for their home or business, the rain gauge may come in handy. Accurate records kept over the course of several years might provide important information about long-term weather changes.