The Seiko 7A48A is a quartz chronograph movement introduced in the mid-1980s, and it is a fascinating evolution of the iconic Seiko 7A-series—specifically building upon the legendary 7A28A and 7A38A calibers. What sets the 7A48A apart is its inclusion of a moonphase complication, making it one of the earliest analog quartz chronograph movements to incorporate astronomical features.

Like its predecessors, the 7A48A is fully analog, built with metal gears, 15 jewels, and independent stepper motors for each chronograph function. It has no plastic parts, no disposable modules, and was designed to be serviced rather than replaced—a rarity in the world of quartz watches.

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Movement Overview

• Caliber: Seiko 7A48A

• Movement Type: Quartz (fully analog chronograph with moonphase)

• Jewels: 15

• Battery: SR927W (Seiko 943)

• Accuracy: ±10 to ±15 seconds per month

• Battery Life: Approx. 2–3 years

• Chronograph Capacity: 60 minutes

• Chronograph Resolution: 1/10 second

The 7A48A is part of the final evolution of the 7A family, and though it shares architecture with the 7A38, its visual identity and added complication make it a collector’s gem.

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Functions and Dial Layout

The 7A48A is admired for its rich dial design, which includes:

• Central hour and minute hands

• Central chronograph seconds hand (sweep)

• 1/10-second chronograph subdial at 3 o’clock

• 60-minute chronograph counter at 9 o’clock

• Small continuous seconds at 6 o’clock

• Moonphase display at 12 o’clock

• No day/date display

Unlike the 7A38A, which features a day-date window, the 7A48A replaces that complication with a detailed moonphase disc, typically with gold and blue coloring. This aesthetic addition is both functional and visually elegant, making the 7A48 watches stand out.

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Chronograph Operation

Like other 7A series movements, the chronograph operates with precision and smoothness:

• Start/Stop: Top right pusher (Button A)

• Reset: Bottom right pusher (Button B)

• Hand calibration: Pushers on the left side (Buttons C and D)

The 1/10-second subdial only activates when the chronograph is stopped, jumping to display the precise recorded time to conserve battery. Timing is accurate to 1/10th of a second for events lasting up to 60 minutes.

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Moonphase Function

The moonphase complication is driven by a gear system that advances the moon disc gradually over a 29.5-day cycle. It is manually set via the crown, typically during the initial time-setting process.

To set the moonphase correctly:

1. Look up the current phase of the moon for your location.

2. Pull the crown to the second click (time-setting position).

3. Rotate the hands forward until the moon disc shows the correct moon phase.

4. Push the crown back in.

Unlike mechanical moonphase watches, the quartz-driven 7A48A is much more accurate over time, with minimal drift.

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Battery and Servicing

• Battery type: SR927W

• Expected life: ~2–3 years

• Low battery behavior: No official end-of-life indicator (EOL), but lagging hands or non-functional chronograph is a sign of depletion.

To replace the battery:

1. Open the case back with an appropriate tool.

2. Remove the old battery using plastic tweezers.

3. Install the new battery, observing correct polarity.

4. If needed, short the AC terminal to the positive battery terminal to reset the integrated circuit (IC).

5. Recalibrate hands using the side pushers.

Always inspect the gasket and restore water resistance if necessary.

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Technical Specifications

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Legacy and Collectibility

The Seiko 7A48A is a rare and refined piece in the 7A chronograph lineage. It was only produced for a limited time and in small numbers. The watches that feature this movement—such as the 7A48-5000 and 7A48-7000—are highly desirable today, especially those in gold-tone or dress configurations.

Its elegant moonphase, durable construction, and historical value make the 7A48A a standout among vintage quartz chronographs.

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Final Thoughts

The Seiko 7A48A is a testament to Seiko’s pursuit of precision, beauty, and engineering excellence during the golden age of quartz. For collectors and enthusiasts who appreciate analog chronographs with an artistic touch, this movement represents one of Seiko’s finest achievements.

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