Diags is a subfolder of the folder where the Cumulus executable is stored. It contains 10 files named cumulus.~og and cumulus.001 to cumulus.009. These represent recent past logs and the current log. These files log many of the actions performed by Cumulus. They will show the Cumulus Files that have been accessed, values found or calculated from log files, before and after values for updates to highs and lows for monthly and annual extreme records, and much more. When you ask for support via the forum, you often need to upload (as a zip) one or all of the diagnostic files.