The method, used at all levels of American football, remains virtually unchanged and unnoticed after 100 years, taking place beyond the scope of the television camera and the focus of the fans until a precise measurement is needed. Even at this time of year, in the midst of the college bowl season and the start of the N.F.L. playoffs, little thought is given to how the 10-yard increments are measured in the country’s most popular sport.

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.