I work as a land surveyor. This job covers many different projects in many different fields, but they all require the same thing. Precise measurements. Before I take measurements, I have to setup a Base Station. The base station is setup over a point that had a GPS unit setup over it previously, and over the span of 6 hours had used Geo-sync orbit satellite data to pinpoint the GPS Unit's exact position on earth down to a thousandth of 1 survey foot. Once the base is established, I set up another GPS unit on it and verify its coordinated and then can use a roving GPS unit to take precise, sub centimeter measurements on construction items of significant importance, such as welds, valves, etc. I take a shot with the rover, it then uses the known position of the base station, and then the position of the satellites, plugs those numbers into an algorithm which in turn will triangulate the exact position of the Rover unit.