Monochromator with C-T optical layout with one grating. Automatic compensatory device for beeline guide abrasion which can improve accuracy of transmission,reduce noise,and extend application life. Scanning can either be manual or instrument controlled via the SSC-3 controlling unit. Widely used in different speciality and industries such as education, science research, plating film machine and air pollution studies. Various configurations of input and output slits are available all with high precision, long application life time and symmetrical adjustment width.