Altimeters are used by many people in a variety of different situations, such as skydiving, flying, and even hiking. The purpose of an altimeter is to give the user a readout of their current altitude. This can be achieved in many different ways, but the most obvious method is to measure the air pressure. By taking into account the current temperature, one can calculate their current altitude. In early aircraft, this was done with analogue meters, rather than digital calculations. They weren't the most accurate, but still worked very well considering what they were being used for. Now, there are many different kinds of altimeters, but for small scale applications, many analogue altimeters are still being used, but technology allows for much more accurate readings. For hiking, being used with a topographical map, a hiker can determine their location. In skydiving, it's very important to know your altitude, as knowing when to pull the parachute is absolutely paramount. For usage in planes, there have been many different kinds of altimeters, but their general purpose has always been to allow pilots to determine their altitude, which can also be useful for determining if weather patterns are affecting the aircraft. The different kinds of digital meters include sonic and radar altimeters, which show relative altitude, meaning the altitude to the ground rather than sea level altitude. While altimeters are useful, they can only really be used in one way: to determine altitude.