Maninblack4612
Tour Winner

Free from your golf club or for the cost of postage only from the R & A, fits nicely into the bag.
Some of the questions in this section of the Forum can be answered in about 30 seconds by using the index of the above book. Some of the answers given to recent questions here have not only been completely wrong but have been given without reference to any rule, just an "I think this is the way it should be". Nobody can be expected to know all the rules but everyone should be aware of when a rule is likely to have been broken & know where to find the answer. I have needed to consult the book out on the course a few times in competition & often when we have been discussing the rules while having a friendly game.
The index is actually very comprehensive and it usually doesn't take long to find what you're looking for. There is, I believe, an iPhone app too but I don't have an iPhone. In some ways the book is easier.
Get one everybody! There's no excuse!