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Figure 2: Structure of the preprocessor 
GEOSCAN uses three inputfiles: 
- a file containing approximate coordinates (name.crd); 
- a file containing observations (name.obs); 
- a file containing program options (name.opt). 
The file containing approximate values is created with the help of interactive 
editor ASCAN. ASCAN allows for the adding of new point identifications, for the 
deletion of coordinates, etc. Figure 3 shows the main menu of this editor. It is 
also possible to insert approximate coordinates by connecting a digitizer to the 
computer using the communication port RS232. 
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