http://www.technologyreview.com/view/515456/physicists-unveil-worlds-most-precise-clock-and-a-twin-to-compare-it-against/

These clocks are so sensitive that they can easily measure the gravitational redshift, in which clocks tick more slowly in more powerful gravitational fields. In other words they can sense changes in height.

The best clocks today are sensitive to changes of many metres or kilometres. The new clock should be able to discern changes of around 1 cm at the Earth’s surface. That will be for applications such as hydrology, geology and the measurement of ice pack changes in climate change studies.