The USPTO published more than 480,000 patent documents in 2007, so it isn't surprising that a few of them contain errors. Last year the PTO issued 23,000 certificates of correction (CCs), or about 12.5% of all issued patents. CCs are issued to correct typographical errors and other minor defects. However, a recent article citing a study published in the India Business Law Journal suggests that the number of defective patents is much, much higher and that uncorrected errors can be an expensive headache for patent owners. Unfortunately, CCs are not searchable in the USPTO website, although the scanned CC is appended to the original patent. CCs are also announced in the USPTO's Official Gazette.