I buy this gp for my honeymoon trip on a cruise liner . I take it on the top deck and plot the ship 's position relative to its sailing along the eastern US Coast -lrb- we sail from NYC to pr , and St Thomas -rrb- . I be able to track we speed and course the entire time . the battery last as long as the box say , about 12 hour straight . the screen be easy to read and the device be simple enough to use . I be impressed .