Imagine a technical specification that reads:

In the text box, enter "O1" (O the letter, not the number zero)

Is there a convention which achieves this explanation more succinctly, or is more immediately clear?

  • If you can reliably control the font which renders the specification (say, in a PDF, or on hard copy), you could use a font which clearly differentiates zero from the letter oh. Many programmers' fonts do this. If you can't reliably control the font, I think @Jim's suggestion is quite succinct and clear.
    – Dan Bron
    Sep 10, 2014 at 18:40
  • Not that you were asking about this, but when needing to be clear in audio communications, phonetic/spelling alphabets were invented for this exact purpose.
    – Patrick M
    Sep 10, 2014 at 20:55
  • 1
    This is really more of a question for UserExperience.SEO/0/1/l/I are ambiguous for any language which uses the Latin and Arabic numerals, not just English.
    – choster
    Sep 10, 2014 at 23:08
  • @choster My question regards how to express the situation in English. Sep 10, 2014 at 23:11

4 Answers 4


You can write:

In the text box, enter the letter O, followed by the number 1.

  • Thank you. I will go with this: In the text box, enter "O1" (the letter O, followed by the number 1). Sep 10, 2014 at 21:01

Use a font in which the number 0 has a diagonal line through it (like the font we use to write questions and answers on this site, though not the font they come out in!). The standard way of telling a letter O from a number 0 in handwriting is to put a slash through the number.

  • Using the preformatted/code block syntax works for this site: 00OO00OO Sep 10, 2014 at 18:39
  • @DigitalChris - How did you do that?! :-) Sep 10, 2014 at 18:42
  • 1
    If you're writing a question or answer it is the "Preformatted text" button (looks like { } ). Or you can just indent the line 4 spaces. To make some inline c0d3 surround the text with backticks (``). Sep 10, 2014 at 18:45
  • 4
    The problem is that unless you can see both together, you may not realize that a zero has a slash through it. In OP's specific example saying, "Enter O1" won't help anyone.
    – Jim
    Sep 10, 2014 at 20:57
  • This won't help. Until the reader sees a zero with a diagonal line, she doesn't know that the font has a slash. Only a typography expert would be able to see "O1" and know for sure that it begins with the letter O. Sep 10, 2014 at 20:57

In some contexts, especially spoken ones "O for Oscar" (or even just "Oscar" - but not here) would be appropriate. Oscar is the word for the letter O in the NATO phonetic alphabet.

  1. A font can be chosen in which zero is displayed as diagonally struck through. The font "Consolas" has this. (Typing your question will have shown you that EL&U uses Consolas - although this does not display in Consolas on the page when the answer is posted.)

  2. When listing by index letter, the convention is not to use upper- or lowercase letter O, (which, in some fonts, may be mistaken for zero) or uppercase I or lowercase letter l (which, in some fonts, may be mistaken for number 1.)

  3. It is usually a mistake to think that, just because all the index letters have indeed been (or are) letters (A2, F6, P13,), your reader will have the intelligence to realise that it is O1 rather than 01.

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