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In Gridiron football, the chain crew (commonly known as the "chain gang") are assistants to the linesman who handle the first down measuring chain and the down indicator box. The members of the chain crew who operate the measuring chain are called rod men and the person who works the down indicator box is called the box man.
The first down measuring chain is used to measure the yards that the offensive team needs to gain a first down. It is a 10-yard metal chain with poles attached to each end. The poles, usually called "the sticks", are almost always covered in bright orange padding.
When a team gains a first down, one of the rod men places one end of the chain on the sideline parallel to the spot of the ball. The other rod man then stretches the chain out to mark the first down line. To ensure an accurate measurement, a clip is usually attached to the chain on the closest 5-yard mark on the field.
The chains will be brought directly onto the field whenever the referee needs an accurate measurement to determine if a first down has been made. A team may also request an accurate measurement to determine how far they have to reach for the first down.
For games at all levels below the NFL, the chain crew operates on the side of the field opposite the press box. In the NFL, the chain crew switches sidelines at halftime; their initial placement is determined by the referee. In stadiums where both teams' benches are located on the same side of the field, the chain crew operates on the opposite sideline for the entire game.
Auxiliary chain crew 
For professional and college football games, an auxiliary chain crew operates on the opposite side of the field. Here, another "stick" and down indicator box is used so that players and officials can also look at the other side of the field to know where the first down line and the line of scrimmage is, respectively. The auxiliary chain crew also includes the drive start indicator, which is placed at the beginning of a team's drive and stays there until they lose possession. This indicator is only used for statistical purposes to calculate the distance of each drive. It looks similar to a "stick", but it has an arrow (or occasionally a large "X") that points in the direction the offensive team is going.
Members of the chain crew are usually picked by the offices of the home team instead of the league or conference that they play in.
All levels of football are believed[by whom?] to currently use the chain crew, with the exception of the unorganized levels of the game such as backyard, touch and flag football, which use their own ad hoc solutions that do not require a manned chain crew.
One notable exception at the professional level was the World Football League of 1974 to 1975, which used a proprietary device called the "dicker-rod," a 90-inch stick that allowed measurements to be made with one person instead of three. The dicker-rod never saw any usage outside the WFL.