Introduction to the Seiko 6F24A

The Seiko 6F24A is a premium quartz analog movement launched in the late 1990s as part of Seiko’s esteemed 6F-series, which represents the pinnacle of Seiko’s high-accuracy quartz engineering. Based on the twin quartz concept pioneered in the late 1970s, the 6F24A offers exceptional precision with ±20 seconds per year, while integrating a perpetual calendar and a 24-hour GMT hand—all in a compact and elegant design.

Used in select Brightz, Credor, and high-end JDM (Japanese Domestic Market) models, the 6F24A movement embodies precision, craftsmanship, and practicality, offering world travelers and professionals a highly functional and beautifully finished timekeeping engine.

Technical Specifications

Core Features

• Perpetual calendar that automatically adjusts for month length and leap years

• 24-hour GMT hand (non-independent, tracks home or reference time)

• Two motors: one dedicated to timekeeping, one to the calendar

• Thermo-compensated twin quartz technology for high stability

• High-end finishing, often with Geneva stripes or mirror polishing under the dial

Setting Instructions

Crown Positions

• Pull to Position 1 and turn:

  • Clockwise: advance the date

  • Counterclockwise: cycle through month and leap year data

• Pull to Position 2 to set time (all hands except calendar stop)

The 24-hour GMT hand is fixed to the main hour hand and moves accordingly—there is no independent jump-hour feature.

Battery Replacement

Battery Type

• SR920SW (Seiko 371) – silver oxide, 1.55V

• Expected battery life: 5 years

Battery Change Steps

1. Open the case back using a case knife or wrench

2. Remove the dead battery using plastic tweezers

3. Insert the new battery, ensuring correct polarity

4. The movement does not require an AC reset—calendar and timekeeping resume automatically

5. Set the correct time and calendar if needed

6. Replace case back and inspect/replace gasket for water resistance

Calendar and GMT Function

Perpetual Calendar

• Automatically adjusts for short months and leap years

• Pre-programmed until February 28, 2100

• During time setting, the calendar continues to track the date in the background

• Month/leap year data is stored using an encoded system, adjustable via the crown

GMT (24-hour) Hand

• Runs synchronously with the main hour hand, providing home or secondary timezone reference

• Useful for travelers, pilots, or users needing a second fixed time zone

• Does not support independent setting, unlike traveler’s GMT watches

Construction and Quality

• 9 synthetic jewels support key friction points and reduce gear wear

• Metal bridges and baseplate, unlike many disposable quartz movements

• Independent stepper motors for time and calendar systems

• Built-in trimmer capacitor for fine-tuning during regulation

• Temperature sensor linked to the quartz oscillator for real-time accuracy adjustment

The 6F24A is designed not as a throwaway module, but as a precision timekeeping engine meant for decades of use.

Maintenance and Servicing

Service Interval

• Battery: every 4–5 years

• Full movement inspection recommended during battery changes

Serviceable Parts

• Calendar mechanism

• Step motors

• Circuit board and coil block

• Gears and hands

Due to the high complexity of the calendar logic and motor coordination, repair is best performed by a Seiko-trained technician. Some models may require full movement replacement if damaged.

Troubleshooting Guide

Watches Featuring the 6F24A

The 6F24A was used in:

• Seiko Brightz GMT Perpetual Calendar watches

• Credor quartz GMT models

• JDM-exclusive pieces with classic or modern styling

• Watches labeled "Perpetual Calendar / High Accuracy Quartz"

These timepieces are now considered collector-worthy, especially in good cosmetic and mechanical condition.

Conclusion

The Seiko 6F24A is a masterclass in quartz engineering, delivering:

• ±20 seconds per year accuracy

• Perpetual calendar through 2100

• GMT functionality for global travelers

• Serviceable, premium-level construction

Built with the mechanical philosophy of traditional horology and the technological benefits of twin-quartz architecture, the 6F24A stands as one of Seiko’s most technically impressive and collectible quartz calibers—a perfect blend of functionality, beauty, and enduring precision.