The most widely used keyboard layout is QWERTY, named as such for the positioning of the keys in the top left row. Christopher Latham Sholes and Carlos Glidden produced the first typewriter featuring the QWERTY layout in 1874 and though there have been minor changes over the past centuries, for the most part it has remained consistent. One of the differences of the original QWERTY layout from the current version was its lack of a “1” key, and consequently “!” key. Instead of typing the numeral one, typists would use the lower-case L (l). To type an exclamation mark, typists would use a period (.), hit backspace, then type an apostrophe (‘) above it. Another key added in later versions was the “=” and “+” key. These symbols were used very infrequently on typewriters as it was generally assumed that Adding Machines were used to do all the mathematical notation. If typists wanted to produce a plus-sign, they would type a hyphen (-), hit backspace, then type a colon (:). When they wanted to type an equal sign, they would type a hyphen (-), hit backspace, and then type an underscore (_). At the start of the QWERTY layout, typewriters were only able to print UPPER CASE letters, as the “shift key” had not yet been introduced. At the end of the 19th century in 1894, The Duplex full keyboard brought lower case letters to the typewriter by featuring separate keys for lower case and UPPER CASE letters. There were twice as many keys with this design which eventually lead to the invention of the “shift key.” The shift key allowed for a consolidated keyboard similar to the first models that only typed capital letters, as well as the use of both lower and uppercase characters with the same key. Additionally, having a shift key allowed the numerical keys to be shared with special characters such as the ampersand (&) and percent (%) signs for further keyboard consolidation. One problem that arose after the shift key was added was that holding down the shift key to type more than one letter at a time was particularly difficult on early typewriters. This lead to the “SHIFT LOCK” key, later to be renamed “CAPS LOCK” by modern typists. Shift lock allowed typists to switch back and forth between lower and upper case characters, as well as numerical andspecial characters with ease.