diff --git a/lib/Simba/CA.pm b/lib/Simba/CA.pm
index ae671a1..420aeee 100644
--- a/lib/Simba/CA.pm
+++ b/lib/Simba/CA.pm
@@ -368,6 +368,11 @@ sub name2gid {
     }
 }
 
+# currently used log levels:
+# 0 - fatal error, backup failed
+# 3 - global progress messages, like start and end of a backup, statistics.
+# 5 - errors which prevent a file from being backed up
+# 10 - progress messages for single files.
 sub log {
     my ($self, $level, $msg) = @_;
     if ($level <= $self->{log_level}) {