Lto Tape Labels What Does The "RD" Stand For When Referring To The RD Thumbwheel On An LTO-4 Tape Drive?

What does the "RD" stand for when referring to the RD thumbwheel on an LTO-4 tape drive? - lto tape labels

I am working on a training video manually download LTO-4 tape drive attached. The procedures of the producer referred to "RD a wheel in the drive. I know what the wheel, so the need to clarify what the RD" means ", and it has no records of the answer.