Golf Rule 9
Information as to Strokes Taken
INFORMATION AS TO STROKES TAKEN: NOTE--any penalty strokes must be included as to the number of strokes a player has taken.
STROKE PLAY--no penalty, but the player who incurred the penalty should inform his marker as soon as practicable of the mistake.
MATCH PLAY--(i) an opponent has the right to ascertain from the player how many strokes he has taken during play of a hole, or how many strokes were taken on a hole just completed.
(ii) if a player incurs a penalty, he is obligated to inform his opponent as soon as practicable. An exception would be if the player is obviously proceeding under a rule that includes a penalty that's observed by the opponent.
PENALTY--if the player fails to inform his opponent of the penalty, the player is deemed to have given wrong information resulting in loss of hole even if the player was not aware he had incurred a penalty.
(iii) During play of a hole, if a player gives wrong information or deemed to have given wrong information, he may correct his error without penalty prior to his opponent playing his next shot. The penalty is loss of hole for the player if the opponent plays prior to the player correcting his mistake for giving wrong information as to how many strokes had been taken.
NOTE--if the player gives wrong information as to the number of strokes taken after the completion of a hole and this affects the opponent't understanding of the result of the hole, the player incurs no penalty if he corrects his mistake before any player plays from the next teeing ground, or in case of the last hole of the match, before all players leave the putting green. If the wrong information is not corrected, the player loses the hole.