HP-35s Roll down question

[Kevin Braun]

Hi Experts,

I am a new owner of an HP-35s and am entering a Moon Lander program:
http://www.hpmuseum.org/software/35moonla.htm

and line: C027 Rv

has me a bit confused, When I am entering the line and I press Rv, I get:
X Y Z T
0.0

And I am not clear on how to proceed. Would someone mind pointing me in the right direction?

Thank you.
KB