Antiques and collectibles dealers and appraisers sometimes use patent dates on objects to assess the approximate age, period authenticity, and rarity. The current United States numbering system began with a patent issued on July 13, 1836, while prior to that date approximately 9957 patents had already been issued. No numbering system should be considered devoid of errors, and the following table is our most precise approximation of issue years and patent numbers for patents issued since 1836. Numbers as displayed in the table are 7 characters padded with leading zeroes where required, and some numbers within a series may be unused. For these and other reasons, the total number of patents granted during a given year cannot be calculated simply by subtracting the number of the first patent issued in one year from the number of the first patent issued in the next year. Reissue patents were not numbered separately until 1838.