[Source] The Graph 18 Surface Locator was a directional transponder used for orientation on a planet's surface.. The transponder is able to locate itself by examining star-charts and measuring solar and lunar degrees, as well as determine planetary north and south. The unit contained over 25,000 planetary maps and could update by connecting to Alliance MasterNav. Roughly the size of a briefcase, the transponder could also be connected directly to a droid's brain.