officials wear green shirts with black shoulders and stripes on the sides with black pants. The NBL logo is atop the breast and a sponsor's name is on the back. Shirts are V-neck, without a collar, and pants lack belts. All officials wear a whistle that is used to stop play as a result of a foul or a violation on the court. Hand signals are used to indicate the nature of the infraction or to administer the game. In higher levels of college and professional basketball, officials wear a timing device on the belt-line called PTS (Precision Timing System). The device is used by on-court officials to start and stop the game clock in a timely manner, rather than waiting for the scoreboard operator (timekeeper) to do so. Positions and responsibilities The officials must ensure that the game runs smoothly, and this encompasses a variety of different responsibilities, from calling the game to player and spectator management. They also carry a duty of care to the players they officiate and to ensure that the court and all equipment used is in a safe and usable condition. Should there be an issue that inhibits the safe playing of the game, then it is the job of the officials to rectify the problem. Quite often, the job of an official surpasses that of the game at hand, as they must overcome unforeseen situations that may or may not have an influence on the game. There are two standard methods for officiating a basketball game, either "two-person" or "three-person" mechanics depending on how many officials are available to work the game. In "two-person" mechanics, each official works either the lead or the trail position. The lead position is normally along the baseline of the court, with the trail position having its starting point at the free-throw line extended on the left side of the court facing the basket. Officials change position often during the game to cover the area in the best possible way. As the game transitions from one end of the court to the other, the lead becomes the trail and vice versa. Between the two positions, each is responsible for a specific part of the court as well as two each of the side, base or back court lines. Officials change position after certain calls (mostly when the lead official calls a defensive foul). This allows officials to alternate