1806. When you give check you must say so aloud.
1807. If check is not called on either side, but subsequently discovered, you must endeavor to recall all the moves back to the period when the check first occurred.
1808. You are not compelled to cry check when you attack the queen.
1809. If you cry check, and afterward alter your determination, you are not compelled to abide by the intention, provided you have not touched the piece.