A portable device comprises a processing unit embedded in the portable device; a transmission module coupled to the processing unit for wireless communication; an inert navigator module coupled to the processing unit for measure geography information, wherein the inert navigator module includes gyro, accelerator or the combination thereof; an electronic map module stored in the portable device or a remote server to provide geography map; a display and an input unit coupled to the processing unit to display the geography map, wherein the geography information of the portable device measured by the inert navigator module is displayed on the geography map to indicate the location of the portable device. A calibrator is coupled to the portable device to calibrate the inert navigator module.