Hi, I'm currently using CM10k and i've noticed that since CM8000 the Reference.OBK as well as it's sister Mentor.OBK which Chessmaster uses as the primary opening book for coaching. It is well done and very helpful EXCEPT of some flaws on it. First, some of the moves and variation has an incorrect "weight". for instance/example; the 1.e4 c5 "2.c3" is weighted 100 while the 2.Nf3 of the same sicilian is weighted 25 if im not mistaken, and this is irrelevant to what you see in the Database where you can see that the 2.Nf3 in sicilian is more frequently used than the 2.c3. And another very very err stuff i've found in the reference/mentor.Obk is that in the sicilian there are two 2...d6 (kindly check your reference.obk) one is weighted 0 and one weighted higher. and each contains some variations that the other doesn't have, and this is very confusing. these are just my example on the problem with the reference/mentor.OBK in CM10k and below, i hope this is fixed on the 11th edition, or perhaps, CM developement team can give us an updated Reference and Mentor.OBK would be appreciated by those who are studying the opening books thoroughly . there are so many other variations that the 'weight' doesn't match database and even in the most played variation all around. thanks