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Interference from immovable obstruction or temporary water - How to take relief when ball not found in abnormal course condition
If your ball has not been found and it is known or virtually certain that your ball came to rest in or on an abnormal course condition on the putting green, you may take relief under Rule 16.1d. You do this by using the estimated point where the ball last crossed the edge of the abnormal course condition on the putting green as the reference point.