Climate may be defined as the synthesis of long-term atmospheric conditions characteristic of a particular place. Consequently, the study of climate relies on sustained records of daily values. However, both location and equipment are variables and precise measurements may not be possible. There are occasions when an estimate rather than a measurement is necessary, as when gauging the unrecorded past or future. The value of applied climatology - the study of the impact of climate - lies in the analysis of measurements and estimates within the context of change.