A self-contained pre-manufactured roof top unit is used to circulate fresh air, heat or cool a building. In embodiments, a document file may be matched using pattern matching methods and may include comparisons with a comparison reference database to improve or accelerate the indexing process. A first validation chunk independently associated with said N data chunks comprises first validation information for verifying accuracy of data recorded in said N data chunks. There is a first resistor coupled between the common gate node and ground.