Miyota Caliber 0S30

Manufacturer	Miyota (Citizen)
Caliber Number	0S30 (sometimes typed as OS3O)
Type	Quartz
Diameter	13.50”’ (30.80mm)
Height	4.13mm
Jewels	0
Battery Cell Number	SR927W (395/399)
Battery Life	Approximately 5 years
Frequency	32,768Hz
Quartz Type	Tuning fork type quartz crystal
Stem	065-441 (tap 10)
Dial Feet	2:30, 9:30
Hand Sizes	1.20mm/0.70mm/0.17mm (small hands also 0.26mm)
Functions	Hours, minutes, central chronograph seconds, 60 minute counter at 12:00, 12 hour hand at 9:00, small seconds at 6:00
Country of Manufacture	Japan
Known Models	Welder K26 (add yours to the comments below…)

The Miyota caliber 0S30 is a quartz chronograph watch movement. You might also see other listings incorrectly refer to this movement at OS3O, but is should be zero-S-3-zero not O.

Accuracy

Miyota claims the accuracy of this movement to be +/-20 seconds/month.

Resetting the chronograph to zero

If your chronograph hand is not resetting to 12:00 or “zero” position, then you can try the following steps:

1. Pull the crown to position 2
2. Press button A to advance the chronograph hand forward until it is lined up with 12:00. If you long-press A, the hand will move forward faster.
3. Push the crown back to position 0

Note: if you push the crown back in to position 0 while the chronograph hand is still advancing forward, then it will stop the chronograph hand and recognize it as zero position. In this case, you will have to start over again.

Changing the Battery

The Miyota caliber 0S30 takes an SR927W (395) battery cell. Miyota states that the estimated battery life is around 5 years. Keep in mind that this is with the chronograph function off. If you use the chronograph daily or leave it running constantly, the battery will drain faster due to the extra energy needed to drive the gears for the stopwatch and elapsed time counters.

To change the battery, the cell slips under a tab (near the + icon) and is held in place by another tab on an arm that flexes slightly. Gently use your tool to slide this arm/tab aside and the battery will pop up. Wedge the new battery under the permanent tab, hold the spring tab aside, press the cell down and let the spring tab return to its place which holds the battery down.

Replacement prices

The average replacement price at the time of this post was from $27.95 – $32.95.

Additional Resources:

• Instruction manual from Miyota
• Official specs from Miyota
• Buy a replacement OS30 movement here

If you have a watch with the Miyota caliber 0S30, please let the community know in the comments below…