Here is the way we read it, hopefully in simple terms. The initial account shows all your refundable and non refundable OBC, credits such as prepaid excursions, and any day one applicable charges. As each day goes on carges appear for items such as gratuities, excursions, wifi, alcohol, spec dining....etc. These charges drain your non-fefundable OBC first, followed by your refundable OBC next. The bill never makes sense on day one but it does by the last night when we print it up using the printer at the customer desk. It is also slid under your door by the steward on last night.