Hi Dangerdaz,
I'm happy to answer any questions.
'Tough' reduces the save by 1. So a standard 5+ save becomes 4+ with the tough attribute. It is not a separate save.
The observation test should have perhaps have been called a camouflage or 'stay unobserved' test, as the figure being observed has to test. Remember in 'Black Ops' a minus is good, as it reduces your roll.
Let's take an example. A model in light brush and in the correct camouflage is in danger of being spotted by a guard at 14". The basic 'save' is 6+. Reduce that by one for the cover (-1), the camo gear (-1) and by the range (-1) gives a 'save' of 3+.
Hope that helps...
Guy