If it's a 1R coin, it will have a diameter of 20mm; if a 1/2R, then only 18mm.
If the coin is a 1R, the date will be either 1789 or 1790 since the legend appears to read (in part) "CAROLUS IV". Though the 1R coin was produced during the years 1789 through 1808, only in those two years ('89 and '90') did the legend reflect the 'IV' versus a 'IIII'.
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