Mamiya RZ 50mm ULD Question.

[Keith Tapscott.]

I have bought a 50mm ULD lens from Ffordes photographic which arrived today.
The lens seems to have been well looked after, but was not in the original box and no any instructions for use.
How is the floating-system ring used?

 

[polyglot]

You focus the lens as per normal, then rotate the floating ring to the approximate distance to the subject.