천자문
From the year 1742 the first 44 characters of the Thousand Character Classic began being used on some "Sangpyeong Tongbo" cash coins to indicate furnace number, while some "Sangpyeong Tongbo" cash coins used Chinese numerals specifically for this purpose, others used this system because of the non-repetitive nature of the Thousand Character Classic it is often used as a numbering system for the numbers 1 to 1000. The characters of the Thousand Character Classic were usually placed at the bottom (often right below the square centre hole) on the reverse side of the "Sangpyeong Tongbo" cash coins.