HP 98568A Installation Instruction page 103

HP 98287 A Graphics Display Station Interface
Make a note that select code 25 (or the alternate select code you chose in
step 5) and select code 31 have been used and are no longer available. Use
the "Select Code Record" form on the Chapter 5, "Interface Cards" tab for
this purpose.
Note
Graphics Display Station installation is covered in Chapter 8,
"Graphics Devices".
Adding Interface Cards 5-7