Sorry for misleading you but observe the picture below.
It's actually a game. Mastermind to be exact. But it's disguised so it does not look like a game.
It's something I made over 6 years ago but decided to rewrite the old code to clean it up.
The download link is here. Follow the instructions to see how the game is played.
Now, if you are really interested in Rate Calculation, may I suggest you ask an accountant? Because I'd rather play than hurt my head :-)