Select your turn and AI strength, then press "Start" button. Graph shows how good the AI seems to be. If the value is big, AI seems to win. If small, you seems to win. You can check the graph after the game though you don't check the "Graph" checkbox. Though you use level 8 or more, hint values are calculated in no more than level 8.
Strength is adjusted by midgame lookahead, endgame lookahead, and depth of perfect searching. If you use high level, the calculation time will be long.