2.7.3-1 Informative Error Messages

When the computer detects an entry error, an error message should be displayed stating the error and possible subsequent operations.

Additional Information:
Error messages should explicitly provide as much diagnostic information and remedial direction as can be inferred reliably from the error condition. Where clear inference is not possible, probable helpful inference(s) may be offered. For example, "Code format not recognized; enter two letters, then three digits" is preferable to "Invalid input." Users should not have to search through reference information to translate error messages.