Seiko Caliber 4S27

Manufacturer	Seiko
Caliber Number	4S27, 4S27A
Movement Type	Automatic, self-winding mechanical
Lignes	11.5”’
Diameter	25.6mm
Jewel Count	28 jewels
Beat Rate / Frequency	28,800 bph / 4 Hz
Lift Angle	Unconfirmed
Accuracy Rating	+25~-15 seconds/day
Power Reserve	50 hours
Rotor Winding Direction	Bi-directional
Hand-Windable?	Yes
Anti-Shock Device	Diashock
Crown Count	2 (3 if the watch has an internal rotating bezel, but that is not related to the movement)
Hand Count	6
Functions	Central hours; central minutes; central sweeping seconds; 24 hour indicator at 9:00; pointer date subdial at 6:00; fanning retrograde day of the week between 1:00 and 4:00
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	Seiko Brightz (Refs: SAGN005, SAGN007, SAGN009, SAGN011, SAGN013, SAGN015) (Add your watch to the comments below…)

The Seiko caliber 4S27 is a multi-functional automatic watch movement with the functionality to track a second time zone.

This is a discontinued movement that was produced between circa 2003 and 2007.

Second Time Zone:

A watch with the 4S27 can be used as a GMT thanks to the combination of a 24 hour indicator (home time) with the ability to independently set the central hour hand forwards and backwards in hourly increments.

In Seiko’s own words:

“Time zone adjustment function enables to adjust the hour hand only in one-hour increments by easy operation without stopping the minute and second hands. It is convenient when adjusting the time based on a different time zone while you travel abroad.” -4S27 instruction manual, page 38

In order to achieve this, simply ensure that the 24 hour subdial at 9:00 is pointing to current hour of your home time zone.

Then, pull the top crown (2:00) out one click and use it to adjust the central hours hand to the hour of your second time zone. When you pull out the top crown, do not be alarmed when the retrograde date hand jumps into a vertical position outside of the indication zone (this is normal).

Finally, press the crown back in and your two time zones are now set.

Power Reserve:

You may find various power reserve quotes on other sites, but the confirmed power reserve of the 4S27 is 50 hours on a full wind.

The rotor winds the watch in both directions when in motion. The crown winding direction is clockwise.

Turning the crown about 40 times will wind the mainspring to full reserve. You cannot overwind the movement.

Wearing the watch at full power reserve ensures more accurate timekeeping.

Similar Calibers:

There is a similar Seiko caliber 4S77 found in the Credor line. The 4S77 has a higher level of finishing, but other than that, there do not appear to be any major differences when compared to the 4S27.

Important Notes:

• Do not attempt the set the calendar when the central hands are between the hours of 9:00 PM and 2:00 AM.
• Do not adjust the minutes backwards (counterclockwise) when the time on the dial is pointing at or around 1:00 AM.

Additional Resources:

• Official instruction manual (pdf)