ABSTRACT
The sextant is a marine instrument designed to measure angles, generally vertical angles in conjunction with astronomical bodies in celestial navigation, to ascertain position lines and determine a ship’s position. It can be used both vertically to measure altitude above the horizon, and horizontally to determine the angle between terrestrial marks such as prominent lights or features marked on a chart used for navigational position fixing. The Tidal Stream Atlases contain tidal stream information detailing the direction and strength of the tides for up to six hours before to six hours after High Water at key shipping areas around the UK such as the Dover Straits. An alternate source of tidal stream information can be found by consulting the legend of a chart where tidal diamonds at various positions on the chart have been recorded and the direction of set and the rates at Neap and Spring Tides tabulated.
