Tennis players are a sensitive bunch, and people like Ron Rocchi are forever trying to soothe them.

Rocchi, an equipment manager at Wilson, runs the racket stringing shop at this year’s U.S. Open. Its Wilson’s first year as on-site stringer, after the Open’s longtime guru of grommets and gut, Jay Schweid, decided to take on other business opportunities. At Rocchi’s shop, down the hall from the player’s lounge, stars and their coaches and handlers stop by with rackets, grips, and strings. And instructions — lots and lots of instructions.

“We just try to accommodate whatever request they have, whether or not somebody might say, ‘Oh, that’s crazy.’ That’s not crazy,” Rocchi said.

Rocchi works with 12 racket stringers from various corners of the planet. Most are full-time professionals; all have strung rackets at the most prestigious tournaments in the world. Some can turn out as many as 40 rackets in a day, though Rocchi prefers to keep that figure closer to 20. They also change butt caps, grips, and grommets. They charge $25 a racket, a price that has not changed in three or four years. Players almost always provide their own strings. For the last few years, the most popular combination has been polyester strings, which are stiff, running vertically and natural gut running horizontally within the frame.

Although several of the tour’s biggest stars — Roger Federer, Andy Roddick, and Andre Agassi among them — employ private stringers, most rely on the service at that week’s tournament. At Wimbledon in July, and now at the U.S. Open, Rafael Nadal, Justine Henin-Hardenne, and Amelie Mauresmo, to name a few, have left their rackets in the hands of on-site stringers.

The science of stringing is a lot more complicated than it might seem. Casual tennis fans are familiar with string tension, measured in pounds in America and in kilos throughout the rest of the world. Many also understand the basic benefits of higher tension (a little less power and a little more spin, which in effect results in more control) and lower tension (more power and less spin). A simple adjustment to a higher tension helped Agassi keep the ball in the court and win his first-round match Monday evening over Andrei Pavel, 6-7(4), 7-6(8), 7-6(6), 6-2.

“I don’t play with a lot of spin,” Agassi said.

But tension is not what it seems. As soon as a stringer ties the final knot on a newly strung frame, tension plummets. By the time you leave your local pro shop, the tension in each string is different, and none of them remain at the tension you asked for. Strings will continue to stretch ad infinitum, until they break.

When Mauresmo brings her racket to one of Rocchi’s stringers and asks for it to be strung at, say, 22 kilos, she’s really asking that the racket be treated exactly as it was the last time it was strung. If the process is repeated precisely, the tension will decline at the same rate, too. Racket stringers do not take the world “precise” lightly. If a stringer takes even a two-minute rest in the middle of a job, the final tension will not be the same as if he had not rested. That means no phone calls, no visits to the restroom, and no sips of coffee until a racket is done. Players invariably bring a batch of rackets, from five to as many as 10. A stringer can’t rest during a batch, either, as one racket would begin to degenerate sooner than the one following it (it’s not uncommon for players to ask stringers to string their rackets in order; essentially, they choose favorites).

Like many of his kind, Rocchi has a background in engineering. The head stringer at Wimbledon this year, Roger Dalton, turned to stringing after a career in the automotive field (he used to testify in court about exploded engines). Both men agreed that racket stringing, while based on science, is just as much pseudoscience and psychology.

“That’s part of what a good racket person is,” Rocchi said. “We don’t expect a professional athlete to speak in scientific terms. If they can tell us what they don’t like, then part of our job is to figure out what they do like.”

No one questions that players have a refined sense of feel, but there is debate about its limits and origins. A player’s ears, rather than his arm, seem to have more to do with what tension he chooses, or whether he plays with or without a shock absorber. A physics professor at the University of Sydney in Australia, Rod Cross, has found that when he asks professionals to hit with rackets strung at different tensions, they rarely can tell whether the racket is strung too tightly or too loosely. If he plugs their ears, they are clueless.

“The sound that resonates on that string bed is what they are most familiar with,” Rocchi said. “That’s why players ping their rackets and say, ‘I like this one better than this one.'”

Stringing illuminates several differences between men and women in the professional ranks. Men, for the most part, are more particular. Agassi, Federer, and others call upon a new racket every nine games, coinciding with a change in balls. Women rarely do this. Dalton and one of his partners at Wimbledon, Glynn Roberts, said Mauresmo generally takes three rackets to the court, one for each set. In the women’s final, in which she defeated Henin-Hardenne, she took four. Women also seem to care less about whether their rackets are strung a precise number of hours before they play. If it rains, they will use the racket the next day, rather than having it restrung, as most men would. On a rainy day like yesterday at the U.S. Open, Rocchi and his crew might work until 2 a.m., and will cut unused strings from dozens of frames. (“It’s painful,” Rocchi said).

Any conclusions about the genetic predispositions of men and women, gleaned from stringing habits, are speculative. Are men more obsessive? More stubborn? Do women become more attached to their rackets? Rocchi did not want to venture a guess.

“I’m just going to do what the player wants us to do,” he said.

These gender stereotypes are not universal. Nadal does not change rackets every nine games, and Rocchi, Dalton, and Rogers all said the 20-year-old Spaniard could not care less whether a racket was strung the day before his match, or two.

“He’s got other things on his mind, I think,” Rocchi said. “I wouldn’t be surprised if he broke a string and just kept hitting.”