An ultra-precise clock (marine chronometer) for naval ships. Around 500 pieces were manufactured at the request of the Imperial Japanese Navy. The maximum daily error recorded was 0.1 seconds. A timepiece of extreme precision was needed to accurately identify the location (longitude) of a ship. The marine chronometer achieves its high precision with a bimetallic balance wheel, special hair spring, detent escapement, fusee, and other mechanisms.

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