Highly accurate handheld GPS pulling in satellite signals from multiple satellites makes it accurate to within 10'. Ideal for marine use as it has an alarm if your anchor gets loose/drifts, MOB (man overboard) button lets you locate immediately anyone who might fall off. Barometric altimeter, electronic compass, 256-color transflective display. Rockerpad design for easy 1-handed use. Includes 128MB microSD memory card for Mapsource data. I used this in the Sacramento Delta for cruising Delta and Sacramento and San Joaquin rivers using Coast Guard beacons and coordinates. 10,000 point track log to retrace your path. Stores 1,000 way points and up to 50 routes. Operates up to 18 hours on 2AA batteries if not plugged into 12V cable. Still in original box with manual,, memory card, USB interface, and cables. All rubber-sealed for great water resistance. No longer have boat so not needed. Great on land too. I've used it for backpacking where there is no cell service.