Grand Seiko 5646

 The Grand Seiko 5646-7010 is a vintage mechanical luxury watch from the early 1970s featuring a high-frequency automatic movement and a sharp, timeless design.

Design and Case

Grammar of Design: The watch follows rules created by chief designer Taro Tanaka. It uses flat, mirror-polished surfaces and sharp angles that catch the light without distortion. [1]
Size: The stainless steel case measures about 36 mm across and 10.7 mm thick. It wears very comfortably on the wrist as a classic dress watch. [1, 2, 3]
Case Back: The back features a gold Grand Seiko lion medallion. [1, 2]

Movement and Performance

Caliber 5646A: It houses an automatic movement running at 28,800 vibrations per hour (Hi-Beat).
Day and Date: It has a practical day and date window at the 3 o'clock position. The text supports both English and Japanese (Kanji).
Power Reserve: The watch runs for roughly 40 to 46 hours when fully wound. [1, 2, 3, 4]

History and Value

Era: Seiko produced this model at the Suwa Seikosha factory between 1971 and 1973. It represents the peak of mechanical watchmaking before quartz watches took over the market. [1, 2]
Market Price: Collectors can find these pieces on secondary platforms like Chrono24 or eBay, with prices generally ranging from $700 to over $3,000 USD depending on condition and servicing
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The main difference between the Grand Seiko 5645 and 5646 movements is that the 5645 features a date-only complication, while the 5646 adds a day-date complication. [1, 2]
Both calibres belong to the historic 56GS family produced in the 1970s and share the same core high-beat architecture. [1, 2, 3]
Shared Specifications
Frequency: 28,800 vibrations per hour (Hi-Beat)
Jewels: 25 jewels
Adjustment: Adjusted to 5 positions and temperatures
Accuracy Standard: Grand Seiko standard (-3/+5 seconds per day)
Features: Automatic winding, manual winding, and hacking seconds [1]
Key Differences
Complications:
• Caliber 5645: Displays only the date at the 3 o'clock position.
• Caliber 5646: Displays both the day of the week and the date. [1]
Shared Vulnerability: Both movements utilize a plastic quickset gear/rocker for the calendar mechanism. Over time, this plastic component can become brittle and break, making a healthy quickset function a key inspection point for collectors today. [1]