The 8R chronograph family was introduced in 2008 to power Seiko's Velatura 2-register chronographs. It is closely related to the 6R20, sharing that calibre's balance, winding, and works, and runs at the same 28,800 vph. The chronograph portion is a module added above the top plate. The 8R39 is identical in specification to the 8R28 but features a Spron 610 balance spring and 9S "Grand Seiko" escapement.
One unique feature of the chronograph is a three-pointed hammer, allowing all three chronograph hands to instantly reset together. This operates on three separate vertical clutches, as each chronograph hand is individually driven. The date also has an instant change mechanism.
|8R28, 8R39||Automatic||Hour, minute, chrono seconds||Date window||Small seconds, chrono hour, chrono minutes||34||45 hours|