The earliest known mechanical pencil was found in the wreckage of HMS Pandora from 1791. The first patent for a refillable mechanical pencil was issued in 1822. Spring-loaded and twist-feed mechanisms were patented in 1877 and 1895, respectively. The 0.9mm lead was introduced in 1938. In the early 20th century, improvements were made in Japan and America that led to the modern mechanical pencil design still used today.