Sholes and Glidden typewriter length. The redesigned platen also introduced the modern spacing functionality (horizontal and axial movement providing letter and line spacing, respectively). The cylindrical platen became "an indispensable part of every standard [typewriter]". By the end of 1872, the appearance and function of the typewriter had assumed the form that would become standard in the industry and remain largely unchanged for the next century. Although the machine possessed a cylindrical platen and what was essentially a QWERTY keyboard, two design elements that would later become essential were lacking: the ability to write in upper and lowercase letters and "visible" print. Although the
Typewriter typed as a "carbon pack" at the same time as the original. In informal applications such as personal letters where low priority was placed on the appearance of the document, or conversely in highly formal applications in which it was important that any corrections be obvious, the backspace key could be used to back up over the error and then overstrike it with hyphens, slashes, Xs, or the like. The traditional erasing method involved the use of a special "typewriter eraser" made of hard rubber that contained an abrasive material. Some were thin, flat disks, pink or gray, approximately in