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Posted in typewriter facts.

Many old typewriters didn’t include a separate key for the numeral 1 or the exclamation point, and some even older ones also lack the numeral zero. Typists who trained on these machines learned the habit of using the lowercase letter l (“ell”) for the digit 1, and the uppercase o for the zero. These characters were omitted to simplify design and reduce manufacturing and maintenance costs, chosen specifically because they were “redundant” and could be recreated using other keys.