Abstract: In this paper,the process of carrying out a DEM international experiment,organized by the ISPRS Commission Ⅲ in 1980 is described.The instrument used is a home-made Computer Controlled Digitel Mapping System including an Image Coordinate Digitizer.It has been found that so far as precision and speed is concerned,our hme-made instrument is superior as compared with other imported instrumnets.The cost is also much lower.