The Grating Form of the Micrometer of a Low-Latitude Meridian Circle

The low-latitude meridian circle is requested to determine the transit time and the apparent zenith distance simultaneously when a star is passing across the meridian of the instrument;and to determine the passage time when a star is passing across the prime vertical of the instrument.According to the influence of grating inclination,this paper discussed the adoptable form of a micrometer's grating for the low-latitude meridian circle.That is a combinative grating composed of vertical and slant slits.And the method to determine the zenith distance along the prime vertical is approached too.