If you are using AC 16 or earlier, use the "Modify Wall Reference Line" command. You may have to add this to your work environment first.
You should add a signature to your profile with your hardware and AC version since answers can vary with either.
HTH
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K