Editing Clock (section)

===Navigation===

Until advances in the late twentieth century, navigation depended on the ability to measure [[latitude]] and [[longitude]]. Latitude can be determined through [[celestial navigation]]; the measurement of longitude requires accurate knowledge of time. This need was a major motivation for the development of accurate mechanical clocks. [[John Harrison]] created the first highly accurate [[marine chronometer]] in the mid-18th century. The [[Noon gun]] in [[Cape Town]] still fires an accurate signal to allow ships to check their chronometers. Many buildings near major ports used to have (some still do) a large [[Time ball|ball]] mounted on a tower or mast arranged to drop at a pre-determined time, for the same purpose. While [[satellite navigation]] systems such as GPS require unprecedentedly accurate knowledge of time, this is supplied by equipment on the satellites; vehicles no longer need timekeeping equipment.