Primary length standard group maintains an iodine-stabilized helium-neon laser as a Thailand’s primary standard of length. The standard wavelength laser is at 633nmm, which can be traceable to the SI unit of length. All 1-dimension measurement carried out by NIMT can be traced to the primary length standard. This includes a gauge block interferometer, line scale interferometer and laser interferometer, as shown in the traceability chard below.