National Check Professional (NCP) Certification Practice Test

What does the aux-us field in the MIRC line of a commercial check identify?

1. Check amount

2. Check serial number

3. Issuer's bank name

4. Drawer's account number

The correct answer is: Check serial number

The aux-us field in the Magnetic Ink Character Recognition (MICR) line of a commercial check is specifically designated to identify the check serial number. This field plays an important role in the check processing system, as it allows for the unique identification of each check issued by the account holder. In a typical MICR line, key information such as the bank routing number, account number, and the check serial number is encoded, enabling banks to efficiently process, sort, and clear checks electronically. The uniqueness of the serial number helps prevent duplicates and aids in tracking and reconciling transactions. This is crucial for both the bank’s internal controls and for ensuring that checks are processed in the correct order. Understanding this aspect of the MICR line is essential for anyone involved in check processing and also for maintaining accuracy in financial transactions.