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Imagine you give someone a card with the code "5SBDO0" on it.

In some fonts, the letter "S" is difficult to visually distinguish from the number five, (as with number zero and letter "O").

Reading the code out loud, it might be difficult to distinguish "B" from "D", necessitating saying "B as in boy," "D as in dog," or using a "phonetic alphabet" instead.

We want to write codes that can always be communicated clearly. What's the biggest subset of letters and numbers that will, in most cases, still look visually unambiguous and sound unambiguous when read aloud?

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This is an interesting question, but it's not really a question about English. You might have better luck asking in a more general-purpose forum, like Yahoo! Answers. Or, you could simply start down the alphabet, adding one letter at a time, but skipping any character which introduced an ambiguity, i.e., A B C D E F G H I J L M N P Q R S T U W X Y Z 3 4. Omitted: K (looks like H); V (looks like U); 1 (looks like I); 2 (looks like Z); 5 (looks like S); 6 (looks like G); 7 (looks like I); 8 (looks like B); 9 (looks like P). –  J.R. Mar 25 '12 at 20:44
Check some car number plate schemes, they tend to avoid visual similarity. For example, 0 but no O, 1 but no I. –  Hugo Mar 25 '12 at 20:47
@Hugo neat idea thank you! –  elliot42 Mar 25 '12 at 20:48
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closed as off topic by FumbleFingers, J.R., jwpat7, MετάEd, waiwai933 Mar 26 '12 at 16:41

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