Seiko 8F56-0040 Perpetual Titanium GMT

The Seiko 8F56-0040. Seiko really knows how to name a watch memorably. Movement reference, dash, meaningless number.

Fortunately, they spend more time on the actual watch and here we have quite a good demonstration:

Is there another watch that offers :

– 20 bar WR
– Titanium alloy construction
– Sapphire crystal
– 24 hour bezel with markings in raised relief
– 24 hour hand with independently adjustable 12-hour hand
– Perpetual calendar
– 10 year battery life
– 20 seconds / year accuracy
– Applied indices on a deeply coloured shimmering dial
– In-house everything
– Cost less than $1000

Well the answer is likely ‘no’ but perhaps more sadly ‘no, not any longer’. The 8F56 caliber having been discontinued. Which is an enormous shame. There are lots of variations of this watch. I like the 24 hour bezel on this one, very nicely executed in raised relief, but there are others too. The movement itself is thin ( the battery is thicker ) but with 4 hands the dial is necessarily set quite deep. In this model, the dial is a satin green hue that refuses to stay the same colour depending on the light :

It deserves better photos than these dire phone snaps. I nickname this watch the Deep Green Forest. It’s a land-focused version of the Rolex Deep Sea, at rather less outlay. ( Quite candidly, irrespective of price, I prefer the dial execution of the Seiko )

As well as the GMT function ( so-called traveller’s GMT ) which permits local time and date to be set without disturbing the running seconds, minutes or 24 hour hand, the calendar is perpetual. So you don’t need to reset the date until 2100. In my case, I do not foresee this as a concern. If my future grand-kids are reading this as part of some cultural history lesson, a.) hello ! and b.) please adjust the date.

To do so, one cannot use the crown. It’s perpetual, so it’s set at the factory. As long as you spend less than 3 minutes changing the battery every 10 years, you’ll never need to set the date. But if you wish, or need to, it is possible to program in the month, date, and leap-year status from the movement itself, after removing the ( screw down ) back. It’s not complicated, but takes about 5 minutes. I can quite imagine the local ‘change your watch battery for 25 quid’ merchants being flummoxed though. The 8F56 service manual is available online direct from Seiko and explains what to do. The current status of the month, date and leap year can be confirmed at any time by quickly pulling the crown out ( after unscrewing it ) one click and pushing it back in. The date mechanism is powered by its own ultrasonic motor and makes a little whir as it flips over.

Under indoor lighting, it looks more blue. But no less dusty :

This movement is one of Seiko’s ‘high beat’ quartz, if you will, operating at 196KHz in place of the more common 32KHz. There were even higher ( much higher ) frequencies in use back in the Cambrian explosion of quartz development, but almost all current movements have settled on 32KHz, or 32768 cycles/second. 32768Hz is half of a 16-bit counter. Start counting at hex 8000 ( decimal 32768) and when the counter rolls over from 65535 to 0, one second has passed.

The ‘trouble’ being that quartz, like most other materials, is temperature sensitive. A given quartz crystal nominally measured to vibrate at 32KHz for a given electrical input will actually vary depending on the temperature. The standard way to engineer around this is the simplest solution : ignore it. Hence the usual +-15 seconds a month or so accuracy for quartz watches.

The more involved way is to map the temperature variance of the quartz crystals and include this map in the watch IC. Then the counter can rollover at a temperature-adjusted number, taken from the map. This system is used in the Rolex Oysterquartz and Grand Seiko quartz and ETA Thermoline movements. This 196KHz movement is not temperature corrected, but still manages a rated 20 seconds a year accuracy.

Not much info on how this is achieved. My own suspicion being that the crystal is smaller ( hence higher vibrational frequency ) and so the percentage ( not absolute ) difference in vibration per temperature change is less than the 32KHz ones. So the percentage count error is less, too. Seiko grow their own quartz crystals so they certainly have the ability to be creative.

Seiko, with the marketing excellence they are known for, make no reference to this high frequency quartz accuracy on the watch itself. It just says “Perpetual Calendar” and “TITANIUM” on the dial, and “Made in Japan”, “20 bar” and the movement ref on the caseback.

Maybe it should be called the Seiko Humble or Deeply Diffident ?

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