Some of the new tractors and combine harvesters have built-in satellite control. The GPS system, as it is called, picks up signals from special satellites in space, and on the basis of these signals, a computer can calculate the tractor's exact position on the ground. It is the same system that is currently used in boats, cars and even by bikers and trekkers.
Using satellite control, the tractor can go on auto-pilot. The only thing the driver needs to do is to turn the tractor around once it reaches the end of the field. After that, he just pushes a button and the computer will automatically guide the tractor to the other end. Actually, the automatic control can follow the plow furrows more accurately than any person. The factory warrants that the system will stay on course within an accuracy of 5 cm.
In the case of combine harvesters, the satellite system is also used to generating a map of the yield produced on each individual area of the field. Later, when the farmer wants to fertilize his soil, the data from the yield map is fed into the fertilizer machine's computer, and it will then spread the fertilizer in accordance with the soil's requirements on the individual areas of the field.