What is the main topic of the passage?

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TOEFL Practice Test: Reading Passage 9 — practice the complete quiz, review flashcards, or try a random question.

Questions Below Refer To The Following Passage.          Early mariners gradually developed ways of observing and recording in their journals their position, the distances and directions they traveled, the (5) currents of wind and water, and the hazards and havens they encountered. The information in these journals enabled them to find their way home and, for them or their successors, to repeat and (10) extend the recorded voyages. Each new observation could be added to an ever increasing body of reliable information.     Ship captains and navigators were not concerned about running into... Show more

What is the main topic of the passage?