Many old typewriters do not contain a separate key for the numeral 1 or the exclamation point, and some even older ones also lack the numeral zero. Typists who learned on these machines learned the habit of using the lowercase letter l for the digit 1, and the uppercase O for the zero. The exclamation point was a three-stroke combination of an apostrophe, a backspace, and a period. These characters were omitted to simplify design and reduce manufacturing and maintenance costs; they were chosen specifically because they were "redundant" and could be recreated using other keys. On modern keyboards, the exclamation point is the shifted character on the 1 key, a direct result of the heritage that these were the last characters to become "standard" on keyboards.