Note that instead of copying all the files of directory len into working directory, you may alternatively set the path variable $SW3D, copy just the history file len-mod.h into working directory, and run it. If the path variable $SW3D is set correctly, all files required for the computation should be checked and copied into working directory sw3d automatically by Perl script chk.pl when running the history file. To set path to the root directory of the SW3D software in global variable $SW3D, edit file go.pl. You can specify, e.g., $SW3D='/cdrom/web/software/sw3dcd??/' (the two question marks ?? stay for the number of the SW3D-CD you wish to use) if the SW3D-CD disk is in your CDROM drive mounted to the directory /cdrom, or $SW3D='/home/username/sw3d-cd/web/software/sw3dcd??/' if the SW3D-CD disk is copied on your harddisk into the directory /home/username/sw3d-cd.