sentences:  These ŭnbyŏng produced from the year 1101 and were engraved with an official state seal to mark them as a legitimate currency which was valid throughout Goryeo.The ŭnbyŏng weighed around one "Kŭn" (斤, ) which is roughly equal to 600 grams, this made them very useful for paying for large transactions.Historians suggest that the ŭnbyŏng primarily used by the aristocratic classes and that were also often involved in the bribing of government officials.