 By the time of the Age of Exploration these tools were being used in combination with a log to measure speed, a lead line to measure soundings, and a lookout to identify potential hazards.Later, an accurate marine sextant became standard for determining latitude and an accurate chronometer became standard for determining longitude.Passage planning begins with laying out a route along a chart, which comprises a series of courses between fixes—verifiable locations that confirm the actual track of the ship on the ocean.