A leading zero is any zero that proceeds a number string beginning with a non-null value. Often, leading zeros are found on non-electronic and LED digital display that contain fixed sets of digits, such as the manual counter, the stopwatch, the odometer and the digital clock. Leading zeros are also generated by many older computer programs when creating values to assign to new records, accounts and other files, and as such are likely to be used by utility billing systems, human resources information systems and government databases. Many digital camera and other electronic media recording devices use leading zeros when creating and saving new files.
Notable problems involving leading zeros include odometer rollover, calendar date formatting issues, apparently illogical alphabetization of filenames in which 1 is followed by 10, 11, 12, 2 followed by 21 22, 23, etc., and various instances of ambiguity between computer systems that generate and require leading zeros and ones that do not.