Scope or rail mounted cheat sheet

There a lot of commercially available choices. Google.
You can fabricate an inexpensive device employing a rattle can painted small retractable magnet (the diameter of which fits in common QD sockets) with a universal joint. Instant in-out and tuck away when not needed; store laminated DOPE card in butt stock pouch. You can use Rite-in-the-Rain notebook paper as well, not as stiff as a laminated card.