Located in downtown of Nanjing, adjacent to the ancient city wall of the Ming Dynasty, Nanjing Rihua Optic-electronic Instrument Ltd. (Refered as to Rihua Co. , below) is one of the earliest manufacturers of optical survey meters with over thirty years of production history. Its products' registered trademark is HUAGUANG. Equipped with advanced production facilities and perfect technology, Rihua Co. , now has 180 employees. Rihua's major products including Type DJ6-1, DJ6-2, DJ6-3 optical theodolite, DS3 series levelling instrument, DSZ3 automatic levelling instrument, ground stereo camera and HYS-photoelectric liquid & plastic limit meter, etc, have been extensively applied in the fields of mining area, geology, irrigation works, electrical engineering, construction, transportation, national defense and scientific research and have been exported to Australia, Brazil and Peru, enjoying high reputation.