Additional Notes

Iain (the author) may have written a superb "game" but he's
rubbish at writting manuals as you have seen.

Somethings he's forgotten to mention the command 

lab0000000000000

is usable, he actually uses it in one of his examples

All it does is label the line that it is on with the number 
held in the numeric section of the code.  VERY, VERY useful for 
jumps




