The R&A and the USGA today issued a joint statement regarding green-reading materials as follows:
The R&A and the USGA believe that a player's ability to read greens is an essential part of the skill of putting. Rule 14-3 limits the use of equipment and devices that might assist a player in their play, based on the principle that golf is a challenging game in which success should depend on the judgement, skills and abilities of the player. We are concerned about the rapid development of increasingly detailed materials that players are using to help with reading greens during a round. We are reviewing the use of these materials to assess whether any actions need to be taken to protect this important part of the game. We expect to address this matter further in the coming months.