During the episode There's no Place Like Home- Part one (E04x12):

Ben, Locke, and Hurley walk toward the Orchid. Ben uncovers a wooden box that includes a mirrow, binoculars, and crackers. Ben uses the mirrow to signal his group (the Others). The return signal is from a mountain top. Locke uses the binoculars to get a better view. Ben and Locke are looking east toward this mountain top (the ocean is behind them). Actually, the mountains are south of Ben and Locke. The reason this is important is that when Ben and Locke part ways in the Orchid station, Ben tells Locke to travel two miles east to meet the group of Others. Ben should have told Locke to travel travel two miles south to meet the group. Below are the screen shots describing this.