1. Navigational History
(Mariners Education/Navigation)

... was registered for a device that would judge the ship's speed by counting the revolutions of a wheel mounted below the ship's waterline. Accurate time-keeping is necessary for the determination of longitude. ...

2. Marine Navigation
(Mariners Education/Navigation)

... or patterns. Longitude (λ) Lines of longitude appear curved in this projection, but are actually halves of great circles. Latitude (φ) Lines of latitude appear horizontal in this projection, but ...