Keychain Sudoku

Features:
1) Modes: 6 levels
2) Large LCD screen: 30 x 40mm
3) Every square contains digits from 1 to 9.

Multifunction:
1) Hint function   
2) Help function
3) Self-setting function      

Manifold playing:
1) Time: total time is 99 minutes, the shorter the better
2) Step: it can count each step you play, the less the better