This is on the subject of investment returns of Unit Trusts.

The easiest way to translate this is bid to bid (BB) means before charges (such as broker fees) and offer to bid (OB) means after charges. So a return on a Unit trust that is calculated OB is the return after all of the charges have been taken into account. Consequently, a 10% BB yields less than a 10% OB, since they still have to subtract all of the charges from the 10%BB. Does that make sense? Sorry, it's kind of hard to explain in a few sentences. Feel free to email me if you need more info.