The Seiko 6R15 automatic movement is a Japanese workhorse movement that can be seen as an affordable answer to the Swiss ETA 2824. Many watches from previous years contain the 6R15, including many Prospex models and some in the SARB and Presage lines.
The 6R15 has 23 jewels, an accuracy rating of -15/+25 seconds, and a power reserve of around 50 hours.
The upgraded 6R35 has replaced the 6R15 in new watches. They are nearly identical in design, build, and performance, except the 6R35, has an upgraded power reserve of 70 hours.
Seiko 6R15 Specifications
| Manufacturer | Seiko |
| Caliber | 6R15, 6R15A, 6R15B, 6R15C, 6R15D |
| Movement Type | Automatic |
| Diameter | 27.40 mm |
| Casing Diameter | 27 mm |
| Height | 5.25 mm |
| Jewels | 23 or 24 (depending on version) |
| Hacking | Yes |
| Hand-Winding | Yes |
| Vibrations Per Hour | 21,600 BPH |
| Shock System | Diashock |
| Regulator | ETACHRON |
| Power reserve | 50 hours |
| Magnetic resistance | 4,800 A/m (60 gauss) |
| Winding direction | Bi-directional |
| Country of manufacture | Japan |
| Known Watches | Prospex, Sumo, Alpinist, SARB, Presage |
Seiko 6R15 Accuracy
The Seiko 6R15 has an accuracy rating of -15/+25 seconds per day. Usually, it performs within this range, and with regulation, can do even better.
Despite this fact, some users do complain about problems with accuracy on this movement (see the section below on Seiko 6R15 Problems).
Seiko 6R15 Problems
Although it should, the 6R15 sometimes does not perform within the specified accuracy rating. Although uncommon, users have complained about the watch running incredibly fast. Many also complain about their 6R15 being magnetized, despite a magnetic resistance rating of 4,800 A/m (60 gauss) which is consistent with other Seiko movements.
My SARB033, which uses the 6R15, was the first watch that ever got magnetized. I noticed it was running extremely fast, an obvious sign of magnetization. Thankfully, demagnetizing is a simple and quick fix.
Sometimes, issues with accuracy in Seiko’s movements can be resolved simply by wearing the watch more often or avoiding wearing it in especially hot or cold conditions. Accuracy issues may also reflect specific wrist movements or indicate that the movement needs servicing.
Setting the Date
1. Pull on the crown until you feel the first click. You will notice that the second hand continues to move.
If your watch says it is between 9 and 1, you will need to first advance the time sufficiently to figure out if you were in the 9 PM to 1 AM block of time.
If you see the date advance, that means you were indeed in that time block. It is vital not to change the date when the time is between 9 AM and 1 PM. So, advance the time to a safe block of time (see the directions below on setting the time), then resume with these steps.
2. Turn the crown counterclockwise to set the date to the previous date. Turn it clockwise if you need to advance the date.
Setting the Time
1. When the second hand reaches 12 o’clock, pull on the crown until you feel the second click. You will see the second hand freeze.
2. Advance the time by turning the crown clockwise, or set the time backward by turning the crown counterclockwise.
Reading the instructions in the official service manual can help you understand how to set the date and time on the 6R15. You may also find this video helpful:
Winding the 6R15
To wind the 6R15, simply unscrew the crown, and turn the crown clockwise until the watch is fully wound.
Typically, 40–50 full rotations of the crown should be enough to fully power the watch’s power reserve.
However, since the watch has an automatic caliber, winding it enough to get it started, typically 10-20 full rotations will be enough to power it up. From there, you can wear the watch on your wrist, and let the automatic rotor do its job – automatically winding the watch as you wear it.
Features and Complications
Hacking
This movement features hacking, which allows the wearer to stop the second hand by pulling out the crown. This allows you to more accurately set the time, down to the exact second.
Hand-Winding
The 6R15 is an automatic movement that can also be hand-wound by rotating the crown clockwise. If you wear the 6R15 regularly, it should not need a lot of manual winding, since it will wind automatically as your arm swings when you walk. 50 hours is an excellent power reserve.
Date
Watches with the Seiko 6R15 not only can tell the time but also the date. As with the time, you can set it by hand using the crown.
Servicing the 6R15
Seiko advises customers to service their watches every 2-3 years. Obviously, this will not be feasible for everyone, but at the very least we suggest you shoot for 3-5 years. The more often you can service your watch, the better it will run and will protect its longevity.
For the 6R caliber series, the Seiko Service Center charges $250. You can also choose to go through an independent watchmaker, however, who might charge more or less.
Regulating the 6R15
The 6R15 can be regulated to greatly improve its accuracy. Although difficult, it is possible to regulate the movement yourself with the right tools, knowledge, a steady hand, and enough patience.
To learn more about regulating the 6R15, you can watch the video below:
Seiko 4R35 vs. 6R15
Like the Seiko 6R15, the caliber 4R35 has a date display, but no day wheel. The 4R35 caliber is a lot less accurate than the 6R15, however, with a rating of -35/+45 seconds. The 4R35’s power reserve of 40 hours is also a little lower than the 6R15’s 50-hour reserve.
Seiko 6R15 vs. 6R35
If you are looking for a movement that is almost identical to the 6R15, but which has a higher power reserve, you can consider the next step up in the 6R series, the 6R35.
The 6R35 takes the power reserve up to 70 hours. That said, its accuracy is a match on paper to that of the 6R15, but the cost is higher.
It is debatable whether that extra cost is worth it. While 70 hours is much higher than 50 hours, 50 hours is already a pretty high power reserve.
There are also a lot of complaints about the real-life accuracy of the 6R35, even after regulation. If anything, the 6R15 seems like it might be more reliable. So, it arguably offers a better value than the 6R35.
Seiko NH35 vs. 6R15
The NH35 movement is the unbranded Seiko 4R35 equivalent that is sold to third parties. It is less accurate than the 6R15 with an accuracy rating of -20/+40 and has a shorter, ~41-hour power reserve.
The NH35 is directly compatible with watch cases that use the 6R15 movement. This makes it a great budget replacement movement if you’d wish to simply swap out the 6R15 rather than pay to get it serviced.
A brand-new NH35 movement can often be found for well under $100.
Seiko 6R15 vs. Miyota 9015
The Miyota 9015, a Japanese workhorse movement comparable to the 6R15, has a slightly lower power reserve of 42+ hours compared to the 6R15’s 50. The 9015 only has one-direction winding (as opposed to the bi-directional winding on the 6R15).
The accuracy of the 9015 is just -10/+30 seconds per day, although many users comment that the real-world accuracy of the caliber can actually be higher than that.
One final notable distinction between the two is the beat rate. The 9015 beats at 28,800 BPH, versus 21,600 BPH for the Seiko. For some, this may be a good enough reason to choose the 9015 over the 6R15, as it’ll have a smoother second-hand sweep.
Seiko 6R15 Manual
For additional information, visit the official 6R15 user manual here.
Watches That Use the Seiko 6R15 Movement
Some watches containing the 6R15 caliber include:
Prospex: Fieldmaster SBDC011, Prospex Diver SPB051J1, Prospex Diver SPB053J1, Prospex Diver SBDC053, Prospex Diver Trans Ocean SBDC047, Prospex Diver Trans Ocean SBDC039, Prospex Thailand Limited SPB029J1 Silver Sumo 200m Diver, Prospex Sumo Pepsi Bezel SBDC057 Diver 200m, Prospex Japan Limited SZSC004 Green Sumo 200m Diver, Prospex PADI Special Edition SPB071J1 Diver, Prospex Limited Edition Sea Green SPB081J1, Prospex Diver SPB077, Prospex Diver SPB079
Sumo: Sumo SPB055J Zimbe Limited Edition Series 4 Automatic Watch, Sumo SBDC027 Prospex Diver Automatic 50th Anniversary Limited Edition, Prospex Sumo PADI SBDC049 Diver 200m Limited 1000 Pcs.
SARB: Seiko Mechanical Alpinist SARB017, SARB033 Black Dial Watch S, SARB035 Ivory Dial Watch
Presage: Presage SPB047, Presage SPB049, Presage Urushi SARX029, Presage SARX011
Seiko 6R15 Price
We have seen a price range of anywhere from $150 to $250 for the Seiko 6R15 movement. This movement is a little easier to come by than the 6R35 (which can make it a good alternative if you cannot find that caliber).
Where to Buy Replacement 6R15 Movements
You can occasionally find replacement 6R15 movements on eBay, however, it is much easier to source a similar Seiko NE15 that is compatible with all watches that use the 6R15.
Summary
The Seiko 6R15 movement can be found in numerous Prospex, SARB, Sumo and Presage watches.
With hand-winding, hacking, reasonably reliable accuracy (especially with regulation), and a 50-hour power reserve, it is easy to see why it was the go-to choice for so many mid-level Seiko watches.
While the 6R35 represents an upgrade with its higher power reserve, the 6R15 is found in watches that are more inexpensive, arguably it making it the better value.
