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After referee Gene Steratore used a decidedly low-tech tool to determine whether the Cowboys gained a crucial first down on Sunday night, there’s been more talk that the NFL needs a high-tech system to figure out whether the ball crosses the line to gain or goal line. Some have suggested taking a cue from tennis, which has a fast and simple replay method for determining whether a ball was inside, on or outside a line.

There’s just one problem: The replay system in tennis wouldn’t work in the NFL.

A spokesman for Hawk-Eye, the company with the patented tennis replay technology, told ESPN in 2015 that its system would be useless in the NFL. The Hawk-Eye system requires a camera that has an unobstructed view of at least 25 percent of the ball. In tennis, that’s easy to do. In football, with 22 players on the field, that’s often impossible: Plays like Dak Prescott‘s quarterback sneak on Sunday night occur with a dozen or more players blocking every possible camera angle.

What about putting chips in the ball to track whether they cross the line? Actually the NFL already does have a chip in each ball. But the data recorded by those chips isn’t available to the officials in real time, and even if it were, it wouldn’t solve much. For starters, the chips don’t provide readings that are accurate down to the millimeter, which they would need to be on a play as close as the Cowboys’ quarterback sneak. And even if the chips were that accurate, they wouldn’t tell us when a player’s knee touched the ground, or when his forward progress was stopped, and those are often the things we need to determine in order to get an accurate spot.

Perhaps some day, technology will allow the NFL to have replay reviews that are as quick and clear as those in tennis. For now, the NFL isn’t ready for high-tech replay.