A typographical error (often shortened to typo), also called a misprint, is a mistake (such as a spelling mistake) made in the typing of printed (or electronic) material. Historically, this referred to mistakes in manual type-setting (typography). Technically, the term includes errors due to mechanical failure or slips of the hand or finger, but excludes errors of ignorance, such as spelling errors, or changing and misuse of words such as "than" and "then". Before the arrival of printing, the copyist's mistake or scribal error was the equivalent for manuscripts. Most typos involve simple duplication, omission, transposition, or substitution of a small number of characters. Fat finger or fat-finger syndrome (especially in the financial sector) is a slang term referring to an unwanted secondary action when typing. When a finger is bigger than the touch zone, with touchscreens or keyboards, there can be inaccuracy and one may hit two keys in a single keystroke. An example is buckled instead of bucked, due to the "L" key being next to the "K" key on the QWERTY keyboard, the most common keyboard for Latin-script alphabets. Marking typos When using a typewriter without correction tape, typos were commonly overstruck with another character such as a slash. This saved the typist the trouble of retyping the entire page to eliminate the error, but as evidence of the typo remained, it was not aesthetically pleasing. In computer forums, sometimes "^H" (a visual representation of the ASCII backspace character) was used to "erase" intentional typos: "Be nice to this fool^H^H^H^Hgentleman, he's visiting from corporate HQ." In instant messaging, users often send messages in haste and only afterward notice the typo. It is common practice to correct the typo by sending a subsequent message in which an asterisk is placed before (or after) the correct word. In formal prose, it is sometimes necessary to quote text containing typos or other doubtful words. In such cases, the author will write "[sic]" to indicate that an error was in the original quoted source rather than in the transcription. Scribal errors Scribal errors received a lot of attention in the context of textual criticism. Many of these mistakes aren't specific to manuscripts and can be referred to as typos. Some classifications include homeoteleuton and homeoarchy (skipping a line due to the similarity of the ending or beginning), haplography (copying once what appeared twice), dittography (copying twice what appeared once), contamination (introduction