chack out the levers for the u900 on the tutorial pages. The cascade box (in simple terms) gives reduced gears such as crawler and super crawler. it also gives you a splitter gear which drops you DOWN half a gear. ie on road work, your mog struggles up a hill in 6th gear, pull the splitter gear leaver forward (towards the windscreen) this gives you 5th plus a half.
the splitter will work on all road gears, this is helpfull when towing heavy loads/ trailers