If the settings "backupstates" and "backupinterval" are set to values larger of zero, automatic backups are saved into the system temp directory. "backupstates" defines how many files are kept and "backupinterval" the time difference in seconds.
The automatically saved files are removed on "File"->"New" ,"File"->"Open", "File"->"Save" or on selecting "No" regarding saving file question on closing the program. Therefore these backup files are only available in case of a software crash or in case of changes that should be undone as long the file was not saved in between.
If a backup file for a currently active calculation should be loaded, this should be done by starting another instance of the software as the backup files are deleted on "File"->"Open".