Modern navigation: Today’s sea navigators are fortunate by comparison with their predecessors. Instead of having to make complex calculations involving times and sextant angles, they can buy a global positioning system receiver. This modern receiver not only provides quick and accurate readings of latitude and longitude, but it also displays the ship’s position on a digital chart. Global Positioning System (GPS): A GPS receiver calculates its distance from a minimum of three satellites by analyzing the different travel times of their signals. The distance from each satellite gives a range of possibilities for the receiver’s location. To find its exact position, a microchip in the on-board receiver calculates where the signals intersect. Satellite network: The global network consists of 24 satellites in six different circular orbits around Earth.The satellites orbit 20,200 km above Earth’s surface. Master control: Located in Colorado, the master control communicates with all the satellites. Range of positions: Each satellite transmits a range of possible positions for the ship. GPS satellite: Each satellite emits precisely timed radio signals. On-board GPS receiver: Today, receivers are made in a range of sizes down to handheld models. They usually give a position accurate to 100 meters, but enhanced units are accurate within 10 meters. Using radar: A radar set displays nearby land, boats, and other surface objects. It is useful for both navigation and collision avoidance, especially in foggy conditions. Charting a course: A navigator normally keeps a record of the ship’s movements on a chart. Positions obtained by GPS or other means are plotted on the chart , which can also be used to work out a compass bearing or a course for the next part of the voyage. Instruments used for charting are nautical dividers and transparent compass. Nautical dividers: Dividers are used for making chart measurements.