The FS_OCD_DOUBLEUNDERLINE_ON box contains the command which enables double-underline simulations for a printer.
The Diconix 150 Plus printer does not support double-underlining; therefore, the FS_OCD_DOUBLEUNDERLINE_ON box is empty.
The HP LaserJet IIP printer does not support double-underlining; therefore, the FS_OCD_DOUBLEUNDERLINE_ON box is empty.