Long before an aerobatic pilot ever ignites the smoke system or rolls inverted, they must learn to respect an invisible monument: the aerobatic box. A precisely defined volume of air, the box is the arena where competition aerobatics has been conducted since the mid-twentieth century. Sanctioned by the Fédération Aéronautique Internationale (FAI), the competition box measures 1,000 meters long by 1,000 meters wide (3,281 feet by 3,281 feet), with both floor and ceiling varying by class—only Unlimited uses a floor as low as 100 meters above ground level. Its upper limit varies by class—highest for Unlimited, lower for Advanced and Intermediate—while the base is sacrosanct; breach it and a boundary judge will mark an infringement that docks precious points from the pilot's score.