Seiko's Speedtimer name has its roots in the 1969 Caliber 6139, the world's first commercially available automatic chronograph. By 1971, the brand's logo was on the hood of the Datsun 240Z, racing through the East African Safari Rally. The SPB515 draws on that heritage with a 39.5mm stainless steel case modeled on the 1972 Speedtimer silhouette, at 12mm the slimmest profile Seiko has produced for its 6R caliber family. The hairline-finish dial is accented with orange on the second hand and the final 15 minutes of the inner countdown bezel, operated by a dedicated crown at 4 o'clock to track pit stop intervals or any other event with a fixed endpoint. LumiBrite hands and markers handle low-light legibility, and the date sits at 4:30. Power comes from the Caliber 6R55, an automatic with manual winding capability, 72 hours of power reserve, and 21,600 vph. Super-hard coating on the steel case and bracelet resists scratching, the curved sapphire crystal carries an inner anti-reflective coating, and water resistance is rated to 660 feet.