HANDS ON: Grand Seiko's tool-tastic steel bezel GMTs


Tyme Master
Founding Member
Jul 17, 2014

HANDS ON: Grand Seiko's tool-tastic steel bezel GMTs

Nov 24, 2021

Time+Tide Watches

I always find it interesting how certain releases seem to fly under the radar. We all remember that watch that grabbed our attention but barely got a peep from the community. Maybe it's bad timing or just bad luck but whatever the case may be, some watches just don't make headlines. However, it tends to be those watches that grab my attention the most. I need to dive in for a closer look. A perfect example of this is these new pair of GMT watches from Grand Seiko that I refuse to let you sleep on. Join me as we break down the SBGM245 and SBGM247.

Read more: https://timeandtidewatches.com/hands-on-grand-seikos-tool-tastic-steel-bezel-gmts/



GMT and sports. A perfect combination.​

The GMT hand allows the time to be read in a second time zone and the hour hand can be adjusted without compromising the watch’s accuracy. This dual-time capability is the perfect function for the world traveler and is here available in a high-performance sports watch. The hour and minute hands are substantial and carry LumiBrite so as to be easily legible, day and night. The GMT hand is in orange and has a distinctive shape that makes it readable at a glance against the green dial. The screw-down crown is recessed at the four o’clock position for extra security and the watch is water resistant to 20 bar. All this, in a case that is just 40.5 mm in diameter. The convenience of GMT meets the high functionality of a true sports timepiece. Quite a combination.


Case Material :Stainless steel
Glass Material :Dual-curved sapphire crystal
Glass Coating :Anti-reflective coating on inner surface
LumiBrite :LumiBrite on hands and index(es)
Case size :Diameter 40.5mm Lug-to-lug 48.6mm Thickness 14.4mm
The perimeter of Band :192mm
Clasp type :Three-fold clasp with push button release

Caliber no. :9S66 Instructions
Movement Type :Automatic with manual winding
Power reserve :Approx. 72 hours(3 days)
Accuracy :+5 to -3 seconds per day (mean daily rate)

Water resistance :20 bar
Magnetic resistance :Equipped
Weight :180.0 g
Other details / Features :
  • ・24-hour hand (dual time display function)
  • ・35 jewels
  • ・Calendar-linked time difference adjustment function
  • ・Date display
  • ・Screw case back
  • ・Screw-down crown
  • ・Stop seconds hand function



Caliber 9S66​

Caliber 9S66 has all the performance of the most standard automatic movement of the 9S mechanical models — Caliber 9S65 — but comes with the addition of the GMT function.
Pulling the crown out by one notch enables the hour hand to be adjusted without stopping the minutes or second hand so that the accuracy is not compromised.

The watch is the embodiment of the Grand Seiko pursuit of high accuracy, maintaining exceptional precision in both the essential time display and the GMT function.


Driving systemAutomatic with manual winding mechanism
Mean daily rate*+5 to -3 seconds per day
Normal usage accuracy+10 to -1 seconds per day
Power reserveApproximately 72 hours
Vibrations28,800 vibrations per hour (8 beats per second)
Number of jewels35 jewels
Features-Dual time function with 24-hour hand
-Quick correction function of time difference adjusting to a calendar
* Mean daily rate is a mean value of daily rates in a condition where the movement before assembly in a case is measured in six positions in a fixed manner under artificially controlled environment for 12 days.



The concept of Grand Seiko was born from the desire to build the world's best watch, and the collection continues to push precision in mechanical watches to the limits of timekeeping technology.

As a true manufacture, Grand Seiko incorporates the latest technology alongside its breadth of craftsmanship to raise the art of watchmaking to its peak.

With anywhere between 200 and 300 individual parts, mechanical watches must exhibit a near-perfect consistency of functionality in the detail of these parts to ensure the precision of the movement. Seiko employs Micro Electro Mechanical Systems (MEMS) technology in the manufacturing of its escapements, bringing the mechanical accuracy of its parts to the forefront of technology.
Mere parts alone, however, cannot constitute the level of precision for which Grand Seiko is renowned.

The task of assembling Grand Seiko is borne by craftsmen and women who have honed their craft to such an extent that they can adjust parts by hand to tolerances of one hundredth of a millimeter. This extremely detailed craftsmanship is what has made possible the very precise timekeeping delivered by the 9S mechanical movement.



Mechanical watches utilize an escapement, a self-contained device that draws its power from the motive force of a mainspring and uses the same power to regulate the speed at which the spring unwinds. It is a system which has remained largely unchanged since moving hands were first used to tell time.
As part of the mechanism, a wound-up mainspring exerts force to turn gears at a set speed as it unwinds. The precision of the system as a whole is dictated by this speed and the escapement mechanism, comprising the balance, pallet fork, and escape wheel.
The pallet fork sets the pace for the revolving escape wheel and it, itself, operates in accordance with the oscillating balance.
The balance rotates back and forth like a pendulum, ensuring that the mainspring unwinds at an even speed and over an extended period of time. In doing so, the balance effects the steady rotation of the hour, minute, and second hands.



Adjusting the hairspring – the key to precise timekeeping​

The hairspring is the core component at the heart of a mechanical watch which governs its precision.

The elegantly coiled hairsprings are akin to living creatures, with an individuality all their own. Our craftsmen and women can identify and work with this variation, inserting pincers into the spaces within the coil to make adjustments by hand with a precision of one hundredth of a millimeter.

The beautiful ripple of a properly adjusted hairspring are enough to bring a smile to the face of any craftsman. To see the spring come alive is to witness the birth of a mechanical watch and the watchmaker’s work transcends manufacturing to become a work of art.



The balance wheel
– a pillar of precision​

The balance wheel serves the important role of ensuring a consistent beat. The part is so critical to the overall precision of every Grand Seiko watch that its weight is adjusted to within tolerances of one ten thousandth of a gram.

Because it is so sensitive, even the slightest temperature change can cause it to expand or contract, potentially leading to distortions in shape.

The 9S mechanical movement minimizes effects of temperature on the balance wheel and preserves overall precision by adding a fourth arm over the usual two or three.

While this attention to detail increases the level of work required in the manufacture of components, Seiko is committed to preventing balance wheel deformation and maintaining ultimate precision.



Polished by hand​

The power must flow between the gears with only minimal loss of energy to assure that the watch performs perfectly over time.

To ensure the efficient transfer of the critical power of the mainspring, Seiko’s craftsmen and women polish the grooves between the gear teeth one by one.

The painstaking but vital polishing of every gear tooth ensures that friction is minimized and that the longevity of every component is extended.


MEMS technology for high precision parts​

Micro-Electro-Mechanical Systems (MEMS) technology is used to fabricate precision parts for Caliber 9S. MEMS, a highly advanced semi-conductor manufacturing technology – makes it possible to produce lightweight parts with extreme precision to tolerances of one thousandth of a millimeter.


Escape wheel teeth tips designed for greater retention of lubrication

Escape wheels manufactured using MEMS technology are 5% lighter than others, which is important as it means that less power is required to turn them and the power reserve is longer.

MEMS also makes possible greater lubricant retention, even at the higher rotation speeds of a high-beat movement, which increases the durability of the escapement.


Pallet fork

Pallet forks manufactured through MEMS achieve a 25% weight reduction due to a change in raw material.



We have more than 50 years of manufacturing experience and know-how in the making of alloys for springs. In 1964, a new material was created, which was later called “Spron”. Spron is a cobalt-nickel alloy, and it has superior elasticity, great strength, and high heat and corrosion resistance. For the development of the hi-beat caliber 9S85, a new Spron alloy was created. Released in 2009, it had taken five years but the result was worth the wait. The “Spron 610” in the new hairspring was more resilient to shock and magnetism and ensures stable accuracy.

By transitioning to this exceptionally hard material, the new hairspring is able to tolerate greater impacts and ensure the precision, minimizing error due to changes in position.



With the reinforced mainspring developed for the 10 beat Caliber 9S85, Grand Seiko achieved the level of torque necessary for a power reserve of up to 55 hours.


Precision beyond that of a chronometer​

The first Grand Seiko, produced in 1960, was awarded official designation as a 'chronometer' according to the highest chronometer standard of the time. It carried the word ‘Chronometer’ on the dial.

Today’s Grand Seiko watches, however, no longer carry this designation because, in the 1970’s Grand Seiko introduced its own, higher, standard. The latest version of this standard, the New GS Standard, was established in 1998 and set standards more stringent than any other.

Some specially adjusted versions of Caliber 9S hold an even greater distinction. Designated with the ‘Grand Seiko Special Standard’, these versions have precision rates of +4/-2 seconds a day.


A 17-day trial​

The 9S mechanical movement is assessed against a unique and rigorous set of standards over the course of 17 days. The movement is tested under various conditions including six different positions and three different temperatures, and its daily variations must fit within very strict tolerance rates in order to merit the status of Grand Seiko.

The pursuit of precision​

Precision. It's the pursuit of every watchmaker. When Grand Seiko was born in 1960, it was ready to break tradition. After meeting the chronometer standards of the time, Grand Seiko set its own accuracy standards in 1966. By 1998, advancements in materials and craft gave rise to the New Grand Seiko Standard. Every movement undergoes rigorous testing in six positions and three temperatures over seventeen days. The craftsmen and women uphold their commitment to quality while consistently exploring the limits of possibility.
The Grand Seiko Standard

ItemUnitGrand Seiko Special StandardGrand Seiko StandardGrand Seiko Standard for women
Mean daily rate* in six positionsSecond / day-2.0 ~ +4.0-3.0 ~ +5.0-3.0 ~ +8.0
Mean variation of daily rateSecond / dayLess than 1.6Less than 1.8Less than 3.2
Maximum daily rate between two consecutive daily rates in the same positionSecond / dayLess than 3.0Less than 4.0Less than 6.0
Variation of rate between positions horizontal and verticalSecond / day-5.0 ~ +7.0-6.0 ~ +8.0-8.0 ~ +10.0
Maximum daily rate between mean daily rate and any individual rateSecond / dayLess than 7.0Less than 8.0Less than 13.0
Variation of daily rate per IC between 8℃ and 38℃Second / day / ℃-0.3 ~ +0.3-0.5 ~ +0.5-0.6 ~ +0.6
Variation of daily rate per IC between 23℃ and 38℃Second / day / ℃-0.3 ~ +0.3-0.5 ~ +0.5-0.6 ~ +0.6
Rate-resumptionSecond / day-4.0 ~ +4.0-5.0 ~ +5.0-6.0 ~ +6.0
Number of positions in inspection6 potisions6 potisions6 potisions
Condition of temperatures in inspection8, 23, 38 ℃8, 23, 38 ℃8, 23, 38 ℃
Length of tests17 days17 days17 days

Mean daily rate*: is a mean value of daily rates in a condition where the movement before assembly in a case is measured in 6 positions in a fixed manner under artificially controlled environment for 12 days.


Automatic GMT SBGM245​

Grand Seiko Sport Collection

USD $5,700


A mechanical GMT with a stainless steel bezel​

SBGM245 is designed to be a go-to for any frequent traveler. The stainless steel case measures 40.5mm in diameter, is rated to 200 meters, and has a magnetic resistance of 4,800 A/m. The bezel is stainless steel and adorned with a 24-hour scale in bold lettering. It is fixed to the case, allowing for the tracking of two time zones.

The blue dial has a vibrant sunray finish. The hands and indexes are multi-faceted, beautifully textured, and feature ample LumiBrite paint for excellent nighttime legibility. The red GMT hand can be adjusted without compromising the watch’s accuracy. It has a distinctive shape that makes it visible immediately against the dial.

SBGM245 runs on caliber 9S66. This is a true GMT movement, which means that the local hour hand is independently adjustable while the GMT hand remains fixed to “home” time. The immediate benefit of this functionality is that upon arriving to a new locale in a different time zone, the owner can simply advance the hour hand forward or backward in one-hour increments to the appropriate time without having to reset the watch.

Caliber 9S66 is rated to +5 to -3 seconds per day (when static), has a duration of 72 hours, and features 35 jewels. Like all Grand Seiko mechanical movements, 9S66 is produced by the highly skilled watchmakers of the Shizukuishi Watch Studio.


Case Material : Stainless Steel
Case Diameter : 40.5mm
Case Thickness : 14.4mm
Case Length : 48.6mm
Lug Width : 20mm
Crown : Screw Down
Strap/Bracelet : Stainless Steel w. three-fold clasp
Crystal : Dual Curve Sapphire
Caseback : Stainless Steel
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