The similarity between "1" and "l", and "0" and "O" was exploited by early typewriters, which typically omitted "1" and "0" on the grounds that they were redundant. Here's an excerpt from the wiki article on typewriters: Many older typewriters did not include a separate key for the numeral 1 or the exclamation point, and some even older ones also lacked 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. A cents symbol (ยข) was created by combining (over-striking) a lower case 'c' with a slash character (typing 'c', then backspace, then '/'). Similarly, the exclamation point was created by combining an apostrophe and a period.[47] 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. I remember being somewhat horrified when I first learned of this. Tom