Grand Seiko Caliber 9S85 Hi-Beat Automatic Movement

Grand Seiko Caliber 9S85

Grand Seiko Caliber 9S85 Hi-Beat Automatic Movement

Manufacturer Grand Seiko
Caliber Number 9S85 / 9S85A
Movement Type Automatic (Hi-Beat), self-winding mechanical
Jewels 37
Power Reserve 55 hours
Vibrations Per Hour 36,000 bph (10 beats/sec)
Hairspring Spron 610
Spron 530
Anti-Shock System Diashock
Rotor Type
Hand Count
Features Central hours; central minutes; central sweeping seconds; date at 3:00
Hacking Seconds?
Country of Manufacture Japan
Known Models SBGR051, SBGH001, SLGH013, SLGH017, SLGH005 (Add your watch to the comments below…)

The Seiko caliber 9S85 (9S85A) is an in-house automatic movement found in various Grand Seiko Hi-Beat models.This member of the 9S series was among the first GS calibers to be released to the USA market. Grand Seiko attributes the possibility of the 9S85 Hi-Beat’s existence to the company’s Spron alloys (discussed below).

In Grand Seiko’s’ own words:

“The challenge of making a high-beat movement is one that only a few watchmakers choose to accept. With its higher oscillation rate of ten beats per second, greater accuracy is achievable, but this increased precision comes at a price because the faster rotational speed can take its toll on the power reserve and even the longevity of the whole movement. Grand Seiko’s 10 beat movement meets these challenges and delivers an accuracy of +5 to –3 seconds a day, a power reserve of 55 hours and the durability for which every Grand Seiko watch is renowned. Caliber 9S85 is the result of many years of development and of advances both in the design and manufacture of components and in the materials themselves.” –Source

Grand Seiko Caliber 9s85

Movement Text:



As a high beat movement with a frequency of 36,000 vph/bph, the cal. 9S85 beats at a rate of 10 times per second. The high frequency of beats (or oscillations) makes this movement capable of being more resistant to shock and accuracy fluctuations, which leads to improved timekeeping performance compared to lower beat rate calibers.

See the video below of the pallet fork and balance wheel in action (actual speed, video was not sped up).

Escape Wheel Design:

You may notice that the escape wheel has a beautiful skeletonized design, but that is not only for cosmetic reasons. The cutouts exists in order to make the wheel lighter in weight (approximately 5% lighter). The pallet fork also has cutouts for the same reason (about 25% lighter than a typical pallet fork). Also, on the escape wheel gear teeth, there are reservoirs (GS also calls them tiered tips) to retain oil more effectively which promotes smoother performance.

Grand Seiko Escape Wheel Mems Technology

These designs were made possible via Seiko’s in-house MEMS technology (a technology used in the semiconductor industry that the Seiko conglomerate is also heavily invested in) allowing for components such as the escape wheel and pallet fork to be produced with extreme precision at tolerances of about 1/10,000 of a millimeter. As Grand Seiko describes it:

“The secret is MEMS. MEMS (Micro Electro Mechanical System) is a technology that allows these critical components to be lighter, smoother and, in the case of the escape wheel of a more intricate design. The new design of the escape wheel featured oil reservoirs at the end of each gear tooth, improving the retention of oil, on which the smooth working of the gear depends.”

Balance Wheel:

Much like the escape wheel and pallet fork mentioned above, the balance wheel was also produced using MEMS precision manufacturing technology. Grand Seiko says the 9S85 balance wheel was machined to “one-millionth of a gram to ensure its precise back and forth rotation”.

Spron 610 Hairspring:

The 9S85 features a Spron 610 hairspring, constructed from an alloy which Seiko says took 5 years to develop (source). “Spron 610” is actually the name of the alloy. It is a metal hairspring, not silicon, but it is still said to be about twice as impact resistant and over 3 times more magnetic resistant than other metal hairsprings.

“Increasing the number of oscillations of the balance wheel leads to a proportionately greater consumption of the mainspring’s energy. Shifting from an 8-beat movement to a 10-beat would require 1.5 times more torque and result in a nearly 40 percent loss of power reserve. Increasing impact resistance and efficiently retaining the energy of the balance spring, which is a part of the balance wheel, is also essential.” –Source

Spron 530 Mainspring:

Caliber 9S85 features another “Spron” alloy in its inner workings, this time in the mainspring. The Spron 530 took Seiko 6 years to develop this proprietary alloy, made specifically for Hi-Beat (10 Beat) movements, to withstand the higher torque needed to tolerate the faster paced oscillation rate.

What Grand Seiko says about it:

“… It delivers about 6% more power than its predecessor and a power reserve of five more hours while maintaining the same degree of corrosion resistance, durability, and magnetic resistance. The new mainspring powers the Grand Seiko 10 beat movement for a remarkable 55 hours when fully wound.” -Grand Seiko (source same as above)

Note: When the 9S85 was first released (circa 2010), the mainspring alloy was Spron 510. Although the current iteration of the movement still seems to be designated as 9S85A (ant not 9S85B as would be expected for evolution in the parts), the current GS catalog lists the mainspring as being made from the newer Spron 530 alloy.


Grand Seiko claims that the calibre 9S85 has an average accuracy rating of -1 to +8 seconds per day in normal conditions and temperatures.

They also provide a “mean daily rate” which consists of the movements being tested in a controlled environment before being installed in a watch case. This testing takes place over the span of 12 days, and in 6 positions before being calculated (remember back to grade school math class: the mean is a method of getting an average by adding up the numbers and dividing them by the number of numbers).

The mean daily rate for the 9S85 is stated by Seiko to be -3 to +5 seconds per day.

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