The Selectric remained unchanged until 1971 when the Selectric II was introduced. Selectric II dual Latin/Hebrew Hadar element IBM replaced the Selectric line with the IBM Wheelwriter in 1984, and transferred its typewriter business to the newly formed Lexmark in 1991. By the Selectric's 25th anniversary, in 1986, a total of more than 13 million machines had been made and sold. Selectrics and their descendants eventually captured 75 percent of the United States market for electric typewriters used in business. The Selectric mechanism was notable for using internal mechanical binary coding and two mechanical digital-to-analog converters, called whiffletree linkages, to select the character to be typed.
The Selectric also replaced the traditional typewriter's horizontally-moving carriage with a roller ( platen) that turned to advance the paper vertically, while the typeball and ribbon mechanism moved horizontally across the paper. The element could be easily interchanged to use different fonts within the same document typed on the same typewriter, resurrecting a capability which had been pioneered by typewriters such as the Hammond and Blickensderfer in the late 19th century. Instead of the "basket" of individual typebars that swung up to strike the ribbon and page in a typical typewriter of the period, the Selectric had an "element" (frequently called a "typeball", or less formally, a "golf ball") that rotated and pivoted to the correct position before striking the paper.
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