<http://io.uwinnipeg.ca/~vincent/ ... ecialRelativity.htm>
The time dilation effect is taken into account every day to help keep the atomic clocks on the 24 Global Positioning System (GPS) satellites that encircle the Earth in sync with Earth-based atomic clocks.
Since the satellites are moving relative to the atomic clocks that are on the ground they have dilated time intervals. The Global Positioning System requires that the satellite clocks be coordinated to a very high accuracy. This is absolutely necessary to predict where the location is of people using the GPS receivers on the Earth's surface. Even though the special relativity effect is very very small, the atomic clocks are accurate enough to be affected by the time dilation effect.