Green reading books have become a big issue on the PGA Tour this year and there is continued debate on whether they should be allowed. During the Northern Trust this issue was heavily discussed on Saturday when Dustin Johnson seemed to look at the book prior to every putt and he took an exorbitant amount of time over many putts. Then on Sunday, both Johnson and Spieth continuously looked at their books and were put on the clock on hole 5 because of slow play.
The commentators mentioned the issue and then the Golf Channel discussed the issue on Monday. I think players are split on the issue, some are OK with the books, others want them banned. Some commentators were fine with the books as long as the players putted within 45 seconds. Unfortunately, the PGA tour has not been inclined to deal with slow play so that is not a solution.
I thought I would show a couple pictures of what the players are looking at in the books. Some players have their own yardage book drawings which vary in detail and descriptions but there are also companies that now provide these books. Below are pictures provided by the companies Green Book and Strackaline. The player still has to take the slope degrees and arrow directions to make a final decision on break, but it is another tool that is quickly becoming a common tool used by PGA players.