A blueback chart was a distinctive type of privately published nautical chart that became the standard for merchant mariners during the 19th century. They are named for the tough, blue manila paper used to reinforce the back of the charts, making them durable enough for use in the harsh conditions of a ship's bridge.
A blueback chart was a distinctive type of privately published nautical chart that became the standard for merchant mariners during the 19th century. They are named for the tough, blue manila paper used to reinforce the back of the charts, making them durable enough for use in the harsh conditions of a ship's bridge.
Source: Wikipedia "Blueback chart" · CC BY-SA 4.0
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