The White Marking Disk for RT MK3.1 Controller (8-Pack) from Teradek works with the RT MK3.1 hand unit. Use this beveled disk for marking focus distances or iris stops. With this pack of eight, you can pre-mark disks with the engraved focus distances on each of your frequently used lenses, saving time on set. Marks from non-permanent and china markers are easily removed; use isopropyl alcohol to clean notations made with permanent markers.