In order to reduce the environment pollution when using field crop spraying machines it is necessary to set the amount of substance correctly and to drive the machine very precise. GPS guiding devices is another new and important way to drive the aggregates correctly. The GPS devices use satellites (up to 20 satellites) to determine the position of the aggregate. The movement and the deviation of the aggregate can be followed on the display mounted in the tractor cabin. Schematically, the operating principle of GPS is as follows: the receiver receives a message transmitted by a satellite; the receiver determines the difference between current time and time at which the message was sent; the receiver calculates the distance between it and satellite, knowing that the signal was transmitted at light speed; the receiver receives another message from two other satellites and calculates the distance between him and satellites; knowing the distance between him and three known points, the receiver calculates its position trilateration method. The signal emitted by the satellites contains data that a receiver uses to calculate the satellite location and make the necessary adjustments for precise positioning. Basic components of an automatic control system for agricultural GPS guidance unit: GPS receiver; user interface that displays errors from the reference line and the main working parameters; algorithms system able to calculate the error from the basic course; the automatic wheel spinner; decoupling sensors for automatic management of danger situations; computer; sensors to compensate the errors induced by the ground irregularities; other sensors needed: speed sensors, sensors for driving in reverse, etc.