To allow the program to work with the files they have to be indexed. During indexing, an index file pertinent to the data file is created, where all the points are sorted according to the prefix and numbers. The points in the data file remain unsorted, in the order they were step-by-step added during the calculations or import.
During the work with the list, the index file is located in the computer memory (for faster manipulation of the list), where the data file is still located on the disc. Therefore, all the changes are immediately stored on the disc
The changes in data are step-by-step written on the disc, while the changes in the index file take place in the operation memory, and the updated index file is normally saved when closing the window with the coordinate list. In case of a compulsory interruption of the program, an updated data file will remain on the disc, but the original index file. According to certain criteria, the program tests the conformity of the data and index files, so it can automatically detect if these two files do not be-long to each other, and in such case automatically creates a new index file.