According to the existing mass spectrometric system, whether or not the informations are sufficient for analyzing substances cannot be judged in the process of measurement. A method for prioritizing a block of data to provide content-based quality of service in a network includes receiving a block of data, selecting a selected rule from a set of available rules, processing the block of data, and prioritizing the block of data. Disposed on the first and second surfaces as well as coupled to the brackets are a set of pulleys which, when used in conjunction with the single rope, allow for a centered stable mounting of the banner.