The boom (1) has a controllable adjusting device that is attached to joints between outer segments (15, 21) and inner segments (17, 19). Sensors (23, 25, 27, 29) and/or angle indicator are attached to the segments for detecting and transferring actual values with respect to relative position. A data processing device (39) is provided with the sensors and/or coupled with the angle indicator. The data processing device provides signals to control elements (3, 5, 7, 9) for adjusting the segments always in relation to the remaining segments. The sensors are formed as ultrasonic sensors. An independent claim is also included for a method for changing relative position of segments of an arm of a spray boom.
