Patent infringement is a two step legal analysis. First, the claims of the patent are construed to determine, as a matter of law, what they mean. Claim construction, or the meaning of the patent claims, is generally determined by review of intrinsic evidence pertaining to the patent. Intrinsic evidence includes the patent itself (claims, specification, drawings), the file history comprising records of the prosecution of the patent before the U.S.P.T.O, prior art made of record during the prosecution, and file history records of any related patent applications claiming common priority to the patent at issue. If claim meaning cannot be determined by the intrinsic evidence, extrinsic evidence may be considered. Extrinsic evidence may include technical dictionaries or treatises contemporary in time to the priority date of the patent and relevant to the particular field or industry, industry use, prior art patents, evidence of what one of ordinary skill in the relevant field knew and/or inventor or expert testimony.