The Seiko 8M25B is an advanced digital quartz movement built for sailing and regatta applications, representing an update to the earlier 8M25A. Retaining the core functionality of a countdown timer, chronograph, daily alarm, and digital timekeeping, the 8M25B improves upon internal logic, energy efficiency, and LCD contrast. The movement is tailored for precision timing during the critical pre-race phase of yacht competitions, making it a specialized tool for skippers and competitive sailors.

Technical Specifications

• Caliber Number: 8M25B

• Movement Type: Quartz (Digital LCD)

• Primary Functions:

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

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

  • Automatic switch to chronograph (stopwatch) after countdown

  • Stopwatch (up to 99 minutes, 59 seconds)

  • Daily alarm

  • Audible signal cues during countdown

• Battery Type: CR2025 lithium cell (3V)

• Battery Life: Approximately 5 years

• Accuracy: ±20 seconds per month

• Display Type: Multi-zone LCD

• Backlight: Available on some models (EL or LED-based)

• Water Resistance: Model dependent, often 100–200 m

• Reset Type: AC (All Clear) required after battery replacement

Key Functions

1. Timekeeping Mode

• Digital display of hours, minutes, seconds

• User can toggle between 12-hour and 24-hour format

• Some models also show day of the week and date

• Precise and stable under normal use with quartz oscillator control

2. Countdown Timer

• Configurable countdown: 1 to 10 minutes

• Audible beep sounds:

  • One beep per minute during countdown

  • Beep every second in the last 10 seconds

• Automatic switch to stopwatch mode once countdown reaches zero

• Ideal for regatta race start sequences

3. Stopwatch / Chronograph Mode

• Counts elapsed time up to 99 minutes 59 seconds

• Can be started manually or triggered automatically after countdown

• Used for overall race time or interval tracking

4. Alarm Mode

• Single daily alarm

• Alarm time is set by hour and minute

• Loud piezo buzzer

• ON/OFF toggle available in alarm mode

Button Configuration

The 8M25B movement is usually installed in watches with four large external buttons for ease of operation, especially while wearing gloves:

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

• B (Bottom Left) – SET: Used to initiate and toggle setting mode

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

• D (Bottom Right) – ADJUST: Used to set time, alarm, or countdown duration

Buttons are spaced and sized to accommodate fast adjustments in wet or active conditions.

Setting Instructions

To Set the Time:

1. Press A to enter Timekeeping mode

2. Hold B until the hour digits flash

3. Use D to change hour

4. Press B again for minutes and toggle 12H/24H

5. Confirm settings with A

To Set the Countdown Timer:

1. Press A to enter Countdown mode

2. Hold B until the minute setting flashes

3. Use D to set the desired countdown time (1–10 min)

4. Press C to start countdown

5. Press C again to pause, B to reset

To Set the Alarm:

1. Press A to enter Alarm mode

2. Hold B until hour digits flash

3. Use D to adjust hour, then B to move to minutes

4. Toggle alarm ON/OFF by pressing D while in Alarm mode

5. Confirm with A

Battery Replacement & AC Reset

Battery Information:

• CR2025, 3V lithium coin cell

• Expected lifespan: 5 years under typical use

AC Reset Procedure:

After battery installation, perform an AC reset to reinitialize the circuit:

1. Open the case back and install the new battery

2. Locate the AC terminal (marked “AC” on PCB)

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

4. Hold for 2–3 seconds

5. Release – the LCD will reset and show all segments briefly

6. Re-enter time and countdown values

Skipping this step may result in blank display or erratic behavior.

Maintenance Notes

• No lubrication or mechanical adjustment is required

• Keep the LCD area and pusher contacts clean

• Replace gaskets during battery changes to maintain water resistance

• Always pressure test if marked “Diver’s” or 200M

• Rinse with fresh water after marine use

Watch Models Using 8M25B

The 8M25B movement was used in a variety of Seiko regatta and marine digital watches, typically found in the Prospex or Marinemaster lines.

Common features of these models include:

• Stainless steel or resin cases

• Large, tactile buttons

• Screw-down case backs

• Water resistance ratings between 100 m and 200 m

• Rubber dive straps or polyurethane bands

Model numbers may start with prefixes like SBBJ, SBEP, or SND depending on the market and case design.

Summary Table

Conclusion

The Seiko 8M25B is a professional-grade digital yacht timer movement, offering sailors and race crews the ability to count down to the start of a regatta, switch seamlessly into stopwatch mode, and maintain accurate daily timekeeping. Designed for use in harsh conditions, it is well-respected among regatta enthusiasts and remains a practical choice in modern marine digital watches. Its intuitive control system, long battery life, and purpose-built design make it one of Seiko’s best sailing-focused quartz movements.