Korean Antique Buncheong ware white inlaid Chinese design plate excavator Joseon Dynasty/1392-1897CE

Lee Dynasty powder blue stone plate with white inlaid Chinese pattern. There is an oxidized earthy smell peculiar to excavated earthenware, but the white inlay is in good condition, and the Chinese pattern remains clearly. The center of the plate is convex. Is it a calligraphy tool? I have never seen a similar product, and it is an exhibition whose purpose is unknown. A wooden box is included.