On 9^th November 2021, our Surveying Division delivered Trimble C5 HP Total station to ITD-RT joint venture in Chinese-Thai Railway project (Map-kabao-Thanon Chira junction) which most of them are tunnels. One of the requirement of the equipment used in surveying and construction the tunnel is accuracy and Trimble C5 HP total station is the answer for this project. With Phase shift EDM Technology, Trimble C5 HP can deliver the high-accuracy distance measurement only 1 mm. + 1.5 ppm in prism mode as it has shorter frequency wave length. The prism mode of Trimble C5 HP is not only the mode that can deliver the higher accuracy than other total station, but also the reflectorless mode. The microscopic laser pointer spot size, just only 26 mm. @30 meters guides users to aim and measure the more accurate distance and position on any surfaces.