The Seiko 8M35A is a specialized digital quartz movement designed for regatta countdown timing. As part of Seiko’s lineup of yacht race watches, the 8M35A combines a programmable countdown timer, auto-start chronograph, and daily alarm into a compact and rugged digital module suitable for competitive sailing. It evolved from previous movements like the 8M25 and 8M32, offering enhanced legibility, improved button control logic, and stronger case integration for marine use.

Technical Specifications

• Caliber Number: 8M35A

• Movement Type: Quartz (Digital LCD)

• Primary Functions:

  • Standard timekeeping (12-hour or 24-hour format)

  • Yacht countdown timer (1 to 10 minutes, adjustable)

  • Automatic switch to stopwatch (chronograph) after countdown

  • Stopwatch (up to 99 minutes, 59 seconds)

  • Daily alarm

  • Audible cues during countdown

• Display Type: Multi-line LCD (segmented)

• Backlight: Present in most models (electroluminescent)

• Battery Type: CR2025 lithium (3V)

• Battery Life: Approximately 5 years

• Accuracy: ±20 seconds per month

• Reset Requirement After Battery Change: Yes – AC (All Clear) reset

• Water Resistance: Depends on model case (typically 100–200 meters)

Key Functions

1. Timekeeping Mode

• Displays hours, minutes, and seconds

• Optional 12-hour (with AM/PM) or 24-hour time format

• Most models also show the day of the week

• Default mode upon powering the watch

2. Yacht Countdown Timer

• Configurable for any value from 1 to 10 minutes

• Audible signals include:

  • One beep every minute during the countdown

  • One beep per second in the last 10 seconds

• At zero, the watch automatically switches to stopwatch mode, helping sailors track total race duration

• Allows easy restarting of races with one button reset

3. Stopwatch / Chronograph

• Time range: 0 to 99 minutes, 59 seconds

• Used for post-start race tracking

• Can be paused and resumed

• Start/Stop controlled via one pusher for simplicity

4. Daily Alarm

• Alarm settable by hour and minute

• Loud piezo buzzer for effective notification

• Alarm toggle available through dedicated function

• Does not interfere with countdown or chrono operation

Button Functions

The 8M35A typically uses a 4-button configuration:

• A (Top Left) – MODE: Cycles through Time → Timer → Chronograph → Alarm

• B (Bottom Left) – SET: Activates setting modes, resets timer or chrono

• C (Top Right) – START/STOP: Starts or stops countdown or stopwatch

• D (Bottom Right) – ADJUST: Used to change values during setting

Buttons are engineered for responsive use, even when wearing sailing gloves. Some cases feature reinforced button guards for impact protection.

Setting Instructions

To Set the Time:

1. Press A to enter Timekeeping mode

2. Hold B until hour starts blinking

3. Use D to change the value

4. Press B to cycle to minutes and 12H/24H format

5. Press A to exit

To Set the Countdown Timer:

1. Press A to enter Timer mode

2. Hold B until minutes flash

3. Use D to set timer (1 to 10 minutes)

4. Press C to start

5. Press C again to pause

6. Press B to reset to programmed value

To Use the Stopwatch:

1. Press A to enter Chronograph mode

2. Press C to start

3. Press C again to stop

4. Press B to reset

To Set the Alarm:

1. Press A to enter Alarm mode

2. Hold B until hour flashes

3. Use D to adjust hour, then press B to set minutes

4. Press D in alarm mode to toggle ON/OFF

5. Press A to confirm and return

Battery Replacement & AC Reset

Battery Information:

• Use only CR2025, 3V lithium coin cell

• Expected battery life: 5 years

Reset Procedure After Battery Change:

1. Open case back and replace battery (observe polarity)

2. Locate the AC terminal on the circuit board

3. Use metal tweezers to short the AC terminal to the battery’s negative pole (case or contact spring)

4. Hold for 2–3 seconds

5. LCD should reset, all segments will briefly illuminate

6. Reprogram time, timer, and alarm settings manually

Maintenance Guidelines

• Movement is fully electronic – no lubrication required

• Clean button contacts and case seals during battery replacement

• Replace gaskets to retain water resistance

• Rinse in fresh water after salt exposure

• Avoid exposure to magnets and hard shocks

Watch Models Using 8M35A

The 8M35A was installed in Seiko’s Prospex Yacht Timer and Marine Master regatta models. Notable features include:

• Full digital display with regatta-specific layout

• Electroluminescent backlight (in most models)

• Resin or stainless-steel construction

• 100–200 m water resistance

• Large side buttons for easy operation during sailing

Reference models may include designations like SBEF0XX or SBBJ0XX, typically offered in both JDM and international editions.

Summary Table

Conclusion

The Seiko 8M35A is a refined digital regatta timer movement, built with the specific needs of sailors and skippers in mind. With a reliable countdown system, auto-switching chronograph, and durable construction, it delivers function-first precision in competitive marine environments. Its long battery life, intuitive controls, and tough digital architecture make it one of Seiko’s most capable quartz yacht timer calibers.