Moon Lander Game for 35s

[Gabor]

I am a beginner in HP programming. I wanted to load the Moon Rocket Lander Game to HP35S but It's not working.

I used this: http://www.hpmuseum.org/software/35moonla.htm

Can You help me:

in line L007 -50 means +/-50 on the calculator keyboard?

also in line C016 -5 means +/-5 ?

in line C020 how can I make "/" ?

M003 INSRUMENT similar to INSTRUMENT?

C027 Rv = R down??

And a last question: How can I check Sum and Length during programming?

Thank You very much for Your help! (I know too little )