A clipboard is a thin, rigid board with a clip at the top for holding paper in place. A clipboard is typically used to support paper with one hand while writing on it with the other, especially when other writing surfaces are not available. The earliest forms were patented in 1870–1871 and referred to as board clips. Another early version of the clipboard, known as the "memorandum file", was invented by American inventor George Henry Hohnsbeen in 1921, for which he was granted U.S. Patent 1,398,591. Related to the clipboard is the Shannon Arch File, which was developed around 1877.