Grand Seiko’s SBGA229 The divers watch combines the precision of traditional mechanical watchmaking and electronic timekeeping. This is made possible by the spring drive technology developed by Seiko and results in an authentic divers watch with a unique inner life. In this feature from the Watchtime archives, with original photos by Olaf Koster, we give it a complete once over.
Grand Seiko is at the forefront of Japanese watchmaking, and the one-of-a-kind spring drive technology is considered the best Seiko has ever produced. So this innovation joins the Grand Seiko collection, which is all about the idea that form follows function and its predecessors from the 1960s. The combination of mechanics and electronics seems perfect, however, and it took several years for the spring drive technology to be integrated into Seiko’s exclusive line.
Seiko introduced spring drive technology in 1999, but the lack of an effective enough automatic winding system and, as a result, the short duration of the power reserve dissuaded the brand from incorporating the technology into the early Grand Seiko. Several years of further development culminated in 2004 in the caliber 9R spring drive. Our test watch included the 9R65 version, which shows the date and remaining power reserve. Its automatic winding system is based on a magic lever: Seiko originally developed this ratchet winding system in 1959 and subsequently improved its efficiency, simplified its maintenance and extended its durability. The power reserve in the hand-wound caliber in the self-winding movement has been extended from 48 hours to 72 hours. Caliber 9R65 is now the most widely used 9R spring drive movement in various Grand Seiko models. Its development was only possible because Seiko had the necessary expertise in both mechanics and electronics.
Spring drive enables high precision
Spring Drive combines the traditional spring power of a mechanical movement with state-of-the-art electronics that do not require a battery or any other external power source. The movement generates its power in a traditional manner, thus making the watch completely independent of external power sources. A mainspring provides power to one end of the gear train. A conventional escapement is replaced at the other end by a regulating system that generates a small electrical charge that activates a quartz oscillator. Instead of an escape wheel, the glide wheel rotates uniformly on an electromagnetic coil, thereby generating an electric current, which is conducted to an integrated circuit (IC) and quartz crystal. As the quartz vibrates at a constant frequency, the IC calculates the required electromagnetic pulse, which controls the rotational speed of the glide wheel and thus the rate of movement. Unlike the escape wheel, the glide wheel is not subject to mechanical interference, so no energy is lost due to friction. A spring drive accordingly achieves a much more accurate rate than a mechanical escapement. Seiko calculates the average deviation to 0.5 seconds per day and a maximum of 15 seconds per month. We measured a deviation of 0.1 second per day on the wrist. After half a month, our test watch increased by 2 seconds.
The spring drive uses quartz technology to control the mechanical movement, thus achieving far greater precision than a purely mechanical movement can achieve. Credit for this accuracy goes to the tri-synchro regulator system, which converts the mainspring’s mechanical energy into electrical current for an integrated circuit and quartz crystal. As the crystal oscillates evenly, the IC controls the rate of the watch by giving impulses to the glide wheel.
A silently gliding seconds hand indicates the seconds
The glide wheel rotates clockwise 28,800 times per hour. This speed corresponds to the number of semi-oscillations completed each hour by balances in modern mechanical movements. But unlike the escape wheel, the glide wheel isn’t repeatedly stopped and released, so the seconds hand moves smoothly around the dial rather than progressing in individual steps. Of course, no ticking sound is produced, but the seconds hand’s silent gliding spring drive makes the time display unique.
A luminous dot glides above the dial at the short end of the second hand. The brightness and constant rotation of this dot are important during a dive because they reassure the wearer that the watch is still running. The hour and minute hands are also richly fitted with LumiBrite, a luminous paint developed by Seiko. These arms are distinctly different from each other as each has its own distinctive shape. Together with the versatile luminescent appliqués, they provide optimum clarity in all lighting conditions that Seiko diving watches are known for.
During the day, the strong black-and-white contrasts beneath the anti-reflective sapphire crystal leave no doubt about the time. The power-reserve display at 8 o’clock looks somewhat unusual: as the power in the mainspring decreases, the hand of this display gradually sweeps up from the bottom in a 90° arc. The white sector below the hand arc indicates when the mainspring is fully wound, but the power-reserve display would be easier to understand if critical stages of declining power reserve were marked by the white segment rather than by the white segment. Gray and then the black part of the arc. The 3 o’clock date is easy to read: this indicator starts changing one hour before midnight and jumps forward to show the next day’s date after midnight. It can be manually adjusted after the crown is removed to its center position.
A professional diver’s watch in a prestigious price class
As befits a diver’s watch, the crown is solid, folded, screwed down and protected from shocks by the lateral sides. The crown is easy to operate in every situation. The unidirectional rotatable divers bezel is equally user-friendly; It snaps smoothly in half-minute increments, is calibrated with markings approximately every minute, and affixed to a case given a special zaratsu polish at Seiko’s Shinshu watch studio. Here, each stainless-steel case is manually polished to a high gloss by gently pressing it against rotating abrasive discs. The bezel is inlaid with titanium carbide, a hard and unbreakable alloy of titanium and carbon. The divers bezel guarantees a secure grip thanks to its ergonomic angle and its notched circumference. Last but not least, the case is pressure resistant to 20 bars and is tightly closed with a massive screwed back adorned with Grand Seiko’s lion emblem.
The deployant clasp, hinged on one side only, is a technical highlight. In addition to lateral push-buttons for closing and opening the safety bow, this clasp also integrates a very functional extension mechanism. Without having to open the clasp, the wearer unlocks the safety and can add more than three centimeters to the length of the bracelet. The extension process progresses gradually through 14 locking points. The bracelet can be compressed again by pushing it back into the clasp. Like the entire stainless-steel bracelet, the clasp is very soft and very comfortable on the wrist.
The manufacturer’s suggested retail price ($6,000) puts the Grand Seiko Spring Drive Diver SBGA229 above the stainless-steel version of Rolex (the undated Oystersteel Submariner $7,500) and Omega’s Seamaster Diver 300M ($5,000). These Swiss brands offer a pressure resistance of 100 meters and, in the case of Omega, greater resistance to magnetic fields. Despite having a technically unique electromechanical caliber, the Grand Seiko will have to struggle to hold its own in such a competitive environment.
Manufacturer: Seiko Epson Corp., Shinshu Watch Studio, Shiojiri, Japan
Reference Number: SBGA229
Duties: Hours, minutes, central seconds, date, power-reserve display, uni-directional rotatable divers bezel
Movement: Caliber Seiko 9R65A based on Caliber 9R spring drive, 28,800 vph (glide wheel), 32,768 Hz (quartz oscillator), 30 jewels, diashock shock absorption, fine adjustment using tri-synchro regulator system, 72-hour diameter 30, mm diameter , height = 5.10 mm
Case: Hardened stainless steel, titanium carbide encrusted bezel, sapphire crystal above the dial, anti-reflective coating on its underside, solid caseback, water resistance up to 200 meters
Bracelet and Cuff: Hardened stainless steel, push-button deployant clasp with safety and extension mechanism
Rate the results (Deviation in seconds per 24 hours):
Average rate: wear test +0.1
Measurements: Diameter = 44.23 mm, Height = 14.12 mm, Weight = 204 g
Variations: Titanium model SBGA031 ($7,100)