It's late in Tokyo's Yurakucho district, and the pachinko parlors clustered here have shut off their garish neon signs. The consoles through which the game's trademark metal balls are sent cascading have gone quiet, and the hard-core players who hang on until closing time are scurrying out onto the pavement to make the last train home.

With the customers gone, it's time for parlor manager Yoshimasa Ono to get down to the most important work of the day: "adjusting" the nails that guide the balls down the consoles' panels, thereby subtly affecting the outcome of a game.

Laboring through the night in this monthly ritual, Ono taps the tiny nails this way and that -- upward just a smidgen to slow the descent of a ball or downward to speed it on its way. Stubborn nails are tamed with the cloven end of an awl-like hand tool. To check his handiwork -- and stave off complaints from players -- Ono runs through the course of each console manipulated to make sure the balls won't get stuck. Now the parlor is ready for another day of business.