When you are working on computers, you MUST use the number '1' and not an upper-case i 'I' because that upper-case 'I' is not a number. The computer won't see it as one. You will lose points. You will have incorrect codes.
The same thing with the ZERO '0' vs the letter 'O' which, by the way, is not acceptable when you are dealing with numbers.
Clear as mud? These two little tips will save some of you some important points off.