On a first down, one end of the chains is placed along the sideline by one member of the seven-person chain gang — hired for game-day duty by the home teams — six feet from the field, supposedly even with the front tip of a football that will be snapped at least 25 yards away. When a play ends, an official estimates the spot, usually marking it with a foot and tossing the ball to another official to set for the next play. When a first down is too close to call, the chains are trotted onto the field.  Sometimes the drive continues by an inch. Sometimes it ends by less.  “There must be a better way,” said Pat Summerall, the longtime N.F.L. player and broadcaster. “Because games are decided, careers are decided, on those measurements.”  There are two sides to the equation. The spot of the ball, now reviewable under the N.F.L.’s replay rules, is often a subject of great consternation. Rare is the debate over whether the chains, not the ball, are in the wrong place.  But every couple of years an inventor patents an alternative to the chains intriguing enough to warrant an audience with the N.F.L.’s competition committee, which debates rules changes.  “I bet you there is some type of technology that comes along in the next five years that creates that change,” said the Falcons’ president, Rich McKay, co-chairman of the committee. “I’m just not sure we have it yet.”  Past ideas have been dismissed, sometimes because of cost, mostly because they were unproven and deemed unnecessary. Tradition is an issue, too. The ritualistic on-field measurement can be a dramatic, momentum-swinging event as anticipated as any pass or handoff.  An official protectively holds the ball against the ground, because precision is suddenly important. The chains arrive from the sideline. An official slowly pulls the chain taut. Breaths are held.  “When we measure, we make sure the players are clear so that TV can get a good shot of the actual measurement,” Pereira said.  Suspense would be lost if every first down were determined instantly.  “There’s a certain amount of drama that is involved with the chains,” said the Giants’ president, John Mara, who is also on the N.F.L.’s competition committee. “Yes, it is subject to human error, just like anything else is. But I think it’s one of the traditions that we have in the game, and I don’t think any of us have felt a real compelling need to make a change.”  In 1906 the Intercollegiate Athletic Association of the United States (now the N.C.A.A.) changed several fundamental rules to reduce football’s violence. Among them were the advent of the forward pass (it remained highly restricted and not a popular option for another couple of decades) and the requirement of 10 yards, not 5, for a first down.  “To assist in measuring the progress of the ball it is desirable to provide two light poles about six feet in length, connected at their lower ends with a stout cord or chain 10 yards in length,” read Spalding’s Official Foot Ball Guide in 1907.  Improvements were imagined almost immediately. In 1929 Luther More of Seattle received a patent for something called Measuring Device for Football Games. It was a contraption with a telescopic “sighting device” that used wheels and pulleys to move along a sideline track.  Early inventors were keen on sights, like those on rifles. Subsequent patents focused on keeping those sights aimed properly, like one in 1967 called a “football liner up device,” using an array of mirrors.  The focus turned toward lasers after a portable hand-held laser system was patented in 1968. In 1973 Willis Pioch of New Jersey received a patent for a “visible line marker” for football fields. Ten yards could be determined by laser beams emitted from boxes along the sideline that slid on rails.  Thirty-five years later, the chains persist. And inventors like Alan Amron, a 60-year-old from Long Island, plan their extinction.  In 2003, with the help of Summerall, Amron presented a sophisticated laser system to the competition committee. Using lasers permanently mounted into stadium lights, a green line — visible to players, coaches and fans in the stadium, and to television viewers — would be projected onto the field to mark the line for a first down. Amron said it would be accurate to within a sixteenth of an inch.  The N.F.L. was intrigued but not interested — yet. There were safety concerns (“I just have visions of lasers being sent all over the place, a ‘Star Wars’ kind of thing,” Mara said last week), although Amron said fears were unfounded. More problematic is that the system costs $300,000 to $500,000 to install in each stadium, Amron said, and has not been tested in an actual game. Attempts have failed for trial runs in an N.F.L. preseason game, or in college football or the Canadian Football League.  “What often happens in these cases when there’s a new proposal, we’re a lot more comfortable if they’ve tested it somewhere else,” Mara said.  Rogers Redding, the secretary-rules editor for the N.C.A.A. football rules committee, said the chain method “may not be superaccurate, but it’s as accurate as you need.”  After all, spotting the ball with an official’s foot and then setting it down across the field is hardly precise, either. The offense’s center often moves the ball before the snap. And, Redding pointed out, who’s to say that the yard lines on the field are perfectly measured in every stadium?  “It’s kind of a diminishing returns thing,” Redding said of reinventing the chains. “How much do you want to invest in this form of accuracy?”  That does not deter Amron and his company, First Down Laser Systems. Amron has a patent for a laser system embedded into the actual sticks attached to the chains. A built-in gyroscope and an automatic level keep the beams pointed straight.  He sees it as a way to prove the validity of the laser concept, perhaps an intermediate step to the stadiumwide system. He hopes for an invitation from the competition committee next spring.  Change, if it comes at all, is years away. But the issue presents itself almost every game.  Trailing the Green Bay Packers late in the fourth quarter of a recent Monday night game at Chicago’s Soldier Field, the Bears faced a fourth-and-1. Running back Matt Forte bulled straight into a scrum.  The ball was placed on the ground and the chains arrived from the sideline. The tip of the ball peeked just past the marker.  Forte scored on the next play, sending the game to overtime. The Bears kept their playoff hopes alive for another week with a winning field goal.  In the aftermath, there was some debate about where the ball was marked on the fourth-down play. No one wondered if the chains were in the right place. After 100 years, why wouldn’t they be?  A version of this article appears in print on , on Page A1 of the New York edition with the headline: In High-Tech Game, Football Sticks to an Old Measure of Success. Order Reprints| Today's Paper|Subscribe
Dozens of inventions would have improved or ended the use of chains to measure for first downs, but they endure.