Seiko Astron GPD: The Most Accurate Watch Ever

Seiko Astron GPS Solar – Most Accurate Watch Ever



Have you ever asked yourself what the perfect watch would actually be? To pontificate over this horological perfection we first need to ask what is a watch actually for. The obvious answer is to tell the time. However, I would hazard a guess that 99% of watches on the planet are not telling the correct time. The reason for this is that watches, even the superquartz variety that are guaranteed to lose or gain no more than 15 seconds per year, are generally not set to an accurate source. They are also not regularly reset to the correct time.
Another ideal for the perfect watch would be for it to have no requirement from the user to supply its energy, whether it is being worn or not. Battery powered watches will need to have a new power source installed every three to five years on average. Mechanical watches either need to be hand wound or require the movement of the user. The latter seems ideal until you realise that you have to wear the watch pretty much all the time and maintain a certain level of movement yourself. Again no where near perfect.

Finally, the ideal watch should maintain the date for its owner and change the time to any one of the 39 local timezones wherever they may travel to on the planet.

So, what if there were such a watch that gained its power from any light source, regularly received an updated correction on its timekeeping and date from atomic clocks and recognised where you were on the planet and set the time accordingly? Allow me to introduce to you the incredible Seiko Astron GPS Solar.

This extraordinary watch’s main claim to fame is that, at the touch of button, it will be able to determine wherever you on the planet and set the time accordingly. This is by the use of GPS (Global Positioning Satellites). These GPS have onboard atomic clocks that are accurate to 1 second every 100,000 years. Therefore, these are accurate to 1 second in every 3.155 x 10^12 seconds. My quick maths equates this to an accuracy of 99.9999999999996831% accuracy. Which is enough I reckon. Or, to put it another way. If the average person was given one of these watches at birth it would have only lost or gained 0.75 milli seconds maximum by the time they passed their watch on to a next of kin in their will.

Now, listen to me carefully because I’m only going to explain this once and there is a lot going on here.


Expose dial to any light. With full power reserve the watch will run for approximately 6 months. The solar panel is also used to sense when the wearer is outside. In this instance the Astron will automatically perform a Time/Time zone check.


The Left Display is used to highlight several items of information:


In normal mode the indicator will show how much power reserve remains. This is a simple F for full and E for empty gauge. This is purely to highlight whether there is enough reserved power for a successful signal reception. The movement of the seconds hand will indicate when the power reserve is getting low. If it jumps every two or five seconds the Astron will be unable to receive a GPS signal to allow it to correct the time or time zone.

At the top of the indicator the “1” and “4+” highlight signal strength when trying to perform a time or time zone check. This indicator is also used to determine whether a time or time zone check was last performed. If the indicator points to “1” then just a time check has been performed. I’m sure you can work the rest out.

At the centre of the display is a plane symbol. If the indicator points to this symbol the Astron is in Flight mode. This is a safety mode which stops all incoming GPS signals that could cause interference with a plane’s onboard electronic systems.
At the very bottom the DST (Daylight Savings Time) is highlighted as being ON or OFF.

There is also a 24 hour indicator at the 6 o’clock position, which can be set to 1 minute increments, and a date aperture at 3 o’clock, which will be automatically set to the nearest timezone during a successful GPS signal reception.

Despite the myriad of functions and checks that can be performed on the Astron only three buttons are used.


Pressing button A and immediately releasing it allows the checking of the DST setting.

Pressing button B and immediately releasing it allows the use to check if the last GPS reception was successful and whether it was for the time only or the time zone. In this instance the second hand will point to the “Y” or “N” on the chapter ring and the “1” or “4+” on the left indicator, for time or time zone, respectively.

Pressing button C and immediately releasing it checks which time zone the watch has been set to. To allow this the second hand will point to the numbers on the outside of the chapter ring. For Example UTC for London and -5 for New York.

Pressing Button A during any of the above checks will return the watch back to normal time display mode.

Receiving a time check GPS signal:
This function is performed automatically should the solar panel within the dial detect that the wearer is outside. However, this function can be performed on demand by following these protocols:

Pressing Button B for 3 seconds. At this point the seconds hand will move to the 12 o’clock position before moving clockwise between the 1 o’clock and 4o’clock position to indicate the GPS reception strength. After about 1 minute the seconds hand will first jump to the “Y” on the chapter ring before moving the correct time. If the seconds hand jumps to the “N” on the chapter ring the GPS signal reception was not strong enough to perform a time check.

NOTE: During December in a leap year (which is when this article was written ironically) the Astron will receive a leap second, which is included to compensate for deviations from the Universal Time (UT), which is astronomically determined, and the International Atomic Time. During this reception the left indicator will point to slightly beyond the “+4” position.

On the one occasion that I did time the GPS reception I simply took two steps from my porch and it took just 38 seconds.

Receiving a time zone check GPS signal:

This is achieved by pressing Button B for 6 seconds. At this point the seconds hand will move to the 6 o’clock position before moving clockwise between the 1 o’clock and 4o’clock position to indicate the GPS reception strength. After about 1 minute the seconds hand will first jump to the “Y” on the chapter ring before moving the correct time zone. If the seconds hand jumps to the “N” on the chapter ring the GPS signal reception was not strong enough to perform a time zone check.

I’ve known owners of so-called radio controlled watches who have really struggled to receive a signal in anything but wide open spaces and whilst they were perfectly stationary. The Astron had no similar issues with receiving a signal. I managed to successfully reset the time in my conservatory and at an outside window. More amazing is that I was also able to perform this whilst in a moving vehicle! The hefty manual that comes with Astron clearly states that there will be areas where reception is more difficult to achieve than others. However, I would have no quarms in recommending this to someone who lived in a built up area.

There is a note of warning in the manual that states that the correct time zone may not be set when you are close to the border of another timezone.

Setting the Astron to Flight mode:

Press button B and then press button C for 3 seconds within 5 seconds of button B being pressed. The second hand will jump to the 8 o’clock position and the left indicator will now point to the plane symbol. Simply reverse the above protocols to turn the Flight Mode off.

Turning the DST On or Off:

Press and release Button A. Then press Button C for 3 seconds within 5 seconds of pressing Button A. The left indicator will change to “ON” or “OFF” and the hour hand will move one hour forwards or backwards, depending on the original DST setting.
Adjusting the time, time zone and date manually (should you be a serious agoraphobic or a speleologist).

To manually adjust the time unscrew the crown and pull it out to the second position. Press button A for three seconds. The seconds hand will move to the 12 o’clock position. Press buttons B or C to adjust the time backwards or forwards.

To set the date unscrew the crown and pull it out to the second position. Now simply press Button B or Button C to advance or return one day.


To adjust the time zone manually press and hold Button C for three seconds. Then simply press button B or C to increase or decrease the time zone, respectively.

Adjusting the 24 hour indicator:


This is simply achieved by unscrewing the crown to the first position and pressing either Button B or Button C. Pressing and holding Button B will start the dial to rotate clockwise. Pressing it again will stop this. Single presses of Button B will move the 24 hour indicator anti-clockwise in 1 minute increments. Utilising Button C will perform the same functionality but in an anti-clockwise direction.

Now, I appreciate that the myriad of protocols above do take quite a lot to consume and digest. However, the Astron is very simple to use with very little practice. As I hinted at during the introduction: The Astron could become autonomous if the user regularly exposes the watch face to sunlight. In this case the Astron will receive all the power it needs to function and will regularly receive time correction updates.
Incidentally, if the Astron is not allowed to receive time updates, for whatever reason, the quartz regulator within the movement is accurate to 1/10th per day, which is still not too shoddy.

Technology and materials:

To achieve all of this Seiko has come up with incredible proprietary technology. Over 100 patent applications were made during the 10 year development of the Astron GPS. Seiko designed a new miniature GPS receiver that requires hardly any energy (about 1/5th of usual receivers) to receive the GPS signals from four or more satellites. To give you an idea of the amount of energy required to receive the GPS signal once is equivalent to the second hand moving 10,000,000 times. This is the equivalent of the seconds hand being propelled for over 3 and half months! The ceramic bezel houses the aerial for the GPS reception. This is to allow the GPS signal to be gained with the least possible power consumption. If the aerial were housed within the steel or titanium case it would require much greater power.

The technology does not stop at the functionality either. The materials are also straight from the R and D department. The high-density titanium utilised in two of three models available has been created by Seiko and is stronger and yet 60% lighter than Stainless Steel. This allows the case and bracelet to weigh a mere 135 grams. It can also be polished to a mirror finish, further adding high end feel of this incredible timepiece. The strap included with the stainless steel version of the Astron is made of a new extra strength silicon material that is stronger and more subtle than other rubber-type straps on the market. I cannot attest to its strength but I can say that that it is very malleable which results in incredible comfort, given the 47mm girth and 16.5mm depth. The silicon strap comes on a double deployment clasp. The sapphire glass has a new “Super Clear-Coating” by Seiko. This may sound like sales babble but in reality this new coating really does make a difference and the superb dial remains legible in the most extreme illumination and at the most acute viewing angles.



The Seiko Astron GPS is available in three variants: The SAST003 which is a standard run all Titanium version, the SAST007, which is a limited edition PVD black Titanium version (see images below) and teh stainless steel SAST009 (highlighted in this review).






The Astron GPS is a thick watch (dimension wise and, most definitely, not intelligence wise). This depth has been put to aesthetically intriguing use with one of the most topographical dials I’ve seen. The hour markers are so visually strong they appear to have structural relevance, like the stanchions of an Olympic Stadium. Each of the 24 hour and flight/DST/power/GPS indicators are also elevated and add yet further ocular interest.





The Solar receiver is just visible under certain light conditions giving the Astron GPS a technical look. However, what is not so immediately obvious, requiring the life-giving sunlight to become apparent, is the wonderful and relevant sunburst effect on the dial. Add to this the optical illusion that the scripts seem to levitate from the dial and it all combines to provide a dial with a lot of visual interest.



Seiko’s luminosity tends to be class leading and the Astron GPS is typical of this. The hands shine green and the hour markers remain their pastel blue throughout the night.



As mentioned above the ceramic bezel was chosen to house the new patented aerial for the GPS receiver, and not just the usual reasons of strength and image.



The caseback is screw down, allowing 100m water resistance. Another impressive figure, which will permit uninterrupted service in harsh conditions, is the 4800A/m magnetic resistance.


One of my personal disappointments is the painted finish on the hands. I appreciate that this is subjective but I feel that the hands would have been more appropriate in the usual polished brass. This would have tied it in nicely with the contrasting polished and satin case and the ceramic bezel. There are so many other high end, well thought out details on this watch, from the applied logo on the dial to the applied and bevel-edged subdial/indicator to the subtle-yet-functional pushbuttons, etc, etc, that the hands simply seem a little out of place.


Also, whilst I’m having a bit of a dig, the silicon strap is extraneously long. I admit that I have below-average 6.5” wrists, due mainly to my below average height. However, I do have reasonably sized 10.5” forearms and the silicon strap fits comfortably round this. Is there anyone out there with 10.5” wrists? Incidentally, I wear the Astron GPS with three holes in the silicon strap remaining. I can understand Seiko wanting to increase the possible client base by offering a range of 4.5 inches in wrist size but it mean that average people are left with superfluous strap. There is a very nicely finished and detailed strap collar. I wonder if Seiko expect wearers like myself to cut the strap down carefully and hide their handiwork under the collar.






I love the Astron GPS and I hate my wrist. For anyone with a wrist size over 7” this really is the most incredible feat of electrical engineering and horology combined. Purists may scoff at the electronics but for those looking for an always-correct timepiece that requires no intervention and which is stress free with regards to the usual issues of power loss due to the battery going flat or the mainspring running down the Astron GPS Solar is most definitely for you.

The technology, materials R and D time, patents and resulting benefits to the user are enough to warrant the asking price in itself. However, I love the design of the Seiko Astron GPS Solar as well. I would be happy and proud to wear this watch, despite my usual bias towards electronic watches, if it weren’t so blummin’ big. 46mm is, sadly, too big for me. The Astron is also a thick watch. Even still, the ergonomics have been well thought out (what hasn’t on this watch?) resulting in a watch that, although looks cumbersome, is very comfortable to wear.


The Astron GPS gives on so many different levels: It is, primarily, a well-built and great looking watch. It also offers interactivity as well as bragging rights down the pub, because no-one else, unless they also own a Seiko Astron GPS, will have the most accurate watch ever created.

The Seiko Astron GPS is one of those timepieces that must have other manufacturers thinking “Now why didn’t we think of that?……Although, if we had would we have been able to create such a watch anyway?”


All words and images by Rick Atkins, unless otherwise stated. This article may not be reproduced part or in whole without the permission of the author.


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