How about a challenge for your class and teacher?
1) Assume that dial starts at zero.
2) Have the Lock ask the user for three numbers.
3) Make the dial do the combination, and then unlock.
Advanced challenge:
1) Make the dial spin past zero twice before stopping at first number.
2) Reverse direction and make the dial spin past first number once before stopping at second number.
3) Reverse direction again, and turn to last number.
All of above worked for me
