Recording goodwill-partnership accounts

Please help me with this. I am confused about the way of recording goodwill in partnership accounts. I am following tulsian's accounts book. The treatment of goodwill as explained in it is very simple like..giving the goodwill in sacrificing/ paying it in gaining ratio in admission/retirement as the case may be by adjusting it through the capital accounts of partners/cash. But I have come across these valuation and premium methods of recording goodwill in in case of retirement of partner in some other book. What's the difference between the two and when to use what?? And one more thing.., when goodwill already appears in balance sheet, as per tulsian's, we just need to write it off and then follow as per the problem. But I have seen a different treatment in some other book where the book value of goodwill is compared with the one given in problem and adjusted. I am not very clear about this! Please do help me with this!:(