The GPS 152 is a 12 parallel channel GPS receiver loaded with a database of American cities and nautical navigation aids such as lights, buoys, sound signals, day beacons and tide data. Built-in memory of one megabyte makes the GPS 152 compatible with Garmin's MapSource Points of Interest CD. With this CD and the GPS 152, you add additional marine navaid detail to your unit. In addition to larger memory, the GPS 152 is compatible with the Wide Area Augmentation System (WAAS), a technology designed to improve the accuracy of GPS positioning to about three meters.On the outside, the GPS 152 comes housed in a waterproof case that's about four inches high and five inches wide. A large four-inch diagonal, high-contrast display features 100x160 pixels for the ultimate in readability. A simple keypad at the bottom of the unit makes entering information easy, without blocking your view of the display.