| Latitude | The distance north or south of the equator. (i.e.) 40" 40´ 56" N |
| Longitude | The distance east or west of the prime meridian or Greenwich meridian. (i.e.) 76" 11´ 46" W |
| A fix | The intersection of two or more crossing lines on a map used to determine position. |
| Dead reckoning (DR) | Using a prior position of the ship´s course and speed. |
| Estimated position (EP) | Correcting the DR position for leeway, the current and steering error. An experienced navigator develops an extremely accurate EP. |
| Pilotage | Navigating within sight of land using geographic (a lighthouse) and/or underwater features (shallow water echo sounders). |
| Sextant | A critical component of modern celestial navigation. Measures the angle formed: at the observer´s eye, a star or the sun, and the horizon. |
| Marine chronometer | Provides accurate time. Is used with the sextant to measure longitude. |
| Global Positioning System (GPS) | Uses about 30 Earth orbit satellites that transmit precise signals. This allows a GPS receiver to determine its location, speed and direction. |
Don't Bet Your Life!
| Delay | GPS signals are sent out only every 12.5 minutes. |
| Atmospheric conditions | Inconsistencies of atmospheric conditions affect the speed of the GPS signals as they pass through the Earth´s atmosphere and ionosphere. |
| Multipath effects | Where the signals reflect off surrounding terrain; buildings, canyon walls, hard ground, etc. These delayed signals can cause inaccuracy. |
| Interference | It is easy for other sources of electromagnetic radiation to desensitize the receiver, making acquiring and tracking the satellite signals difficult or impossible. One example is solar flares. |
| Jamming | Man-made interference can also disrupt, or jam, GPS signals. |
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