-1.9 can enter any system
-2.0 or worse cannot enter 1.0 systems
-2.5 or worse cannot enter 0.9 systems
-3.0 or worse cannot enter 0.8 systems
-3.5 or worse cannot enter 0.7 systems
-4.0 or worse cannot enter 0.6 systems
-4.5 or worse cannot enter 0.5 systems