+dit(bf(--size-only)) Normally rsync will skip any files that are
+already the same length and have the same time-stamp. With the
+--size-only option files will be skipped if they have the same size,
+regardless of timestamp. This is useful when starting to use rsync
+after using another mirroring system which may not preserve timestamps
+exactly.
+
+dit(bf(--modify-window)) When comparing two timestamps rsync treats
+the timestamps as being equal if they are within the value of
+modify_window. This is normally zero, but you may find it useful to
+set this to a larger value in some situations. In particular, when
+transferring to/from FAT filesystems which cannot represent times with
+a 1 second resolution this option is useful.
+