Until the 20th century, the most sophisticated navigational tools and techniques available - dead reckoning using the magnetic compass, marine chronometer (to calculate longitude) and ships logbook (which recorded the vessel's heading and the speed measured by log) or celestial navigation using marine chronometer and sextant - were sufficiently accurate for journeys across oceans, but these techniques (and in many cases also the charts) lacked the precision to avoid reefs close to shore.
