The DCMT (Danish-Chinese Meridian Telescope) is jointly developed by the Shaanxi Astronomical Observatory, Nanjing Astronomical Instrument Factory and Copenhagen University Observatory. The instrument was set up at the Shaanxi Astronomical Observatory in 1990 and put in testing operation in the same year. The design of this horizontal meridian circle is very compact and allows direct real-time monitoring of the instrument parameters. We have studied the stability of the instrument and internal refraction in the telescope tube.