The correction tape was changed independently from the typing ribbon. There were two types of correction tapes: the transparent and slightly adhesive "Lift-Off" tape (for use with the correctable film ribbon), or the white "Cover-Up" tape (for cloth, Tech-3, and carbon film ribbons). This produced typing quality equal to the carbon film ribbon, but with a pigment designed to be easily removed from paper. A new ribbon type, the Correctable Film ribbon, was introduced at the same time. The carriage on this machine held both the main typing ribbon cartridge and two small spools for a correction ribbon. It added an internal correction feature to the Selectric II, intended to eliminate the need for typists to use cover-up tape, "white-out" correction fluid, or typewriter erasers. In 1973 the Correcting Selectric II was announced.
In a few cases the same typeface was available in both pitches, for example, "Courier 72" was the 10-pitch variant of "Courier 12". Separate elements were available for each pitch. The Selectric II was available with a Dual Pitch option to allow it to be switched (with a lever at the top left of the "carriage") between 10 and 12 characters per inch, whereas the Selectric I was ordered with one "pitch" or the other.
However they differed from each other in many respects: These machines used the same 88-character typing elements. The original design was thereafter referred to as the Selectric I. 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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