 The symbol is described as the "number" character in an 1853 treatise on bookkeeping, and its double meaning is described in a bookkeeping text from 1880.The instruction manual of the Blickensderfer model 5 typewriter () appears to refer to the symbol as the "number mark".Some early-20th-century U.S. sources refer to it as the "number sign", although this could also refer to the numero sign.